Single Vertical Fold - Basic: Worksheet 6 - Intermediate-Advanced Practice Single Vertical Fold - Basic INTERMEDIATE ADVANCED

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Configuration:
- Square paper folded vertically right to left
- Right half folds over left half
- Creates 2-layer structure with vertical symmetry

Step 2 - Geometric Relationships:
- Fold line: vertical center line
- Symmetry: Left-right reflection
- Layer alignment: Perfect overlap

Step 3 - Punch Position Analysis:
- Location: center of the folded edge
- In folded state: at the physical edge center
- Important: This is actually the original center line
- Punch affects both layers identically

Step 4 - Unfolding Transformation:
- Unfold right half back to original position
- Hole on right half stays at center line
- Hole on left half mirrors to same position (center line overlap)
- Result: Two holes close together near vertical center line

Step 5 - Pattern Analysis:
- Two holes extremely close together
- Both near the vertical center line
- Almost overlapping but technically separate
- Result: Two holes close together near vertical center line

Advanced Insight: When punching exactly at the fold line in folded state, you get two holes that appear very close to each other when unfolded, not at the same spot.

Verification: Test with physical paper to confirm this non-intuitive result.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.

Complete Solution with Visualization:

Step 1 - Paper Setup:
- Original shape: Square transparent sheet
- Fold type: vertical (left to right)
- Creates: 2 overlapping layers
- Orientation: Left half folds over right half

Step 2 - Fold Analysis:
- Vertical fold creates left-right symmetry
- Mirror axis runs vertically through center
- Left and right halves overlap perfectly
- Each point has a mirror counterpart

Step 3 - Punch Operation:
- Location: upper section of folded paper
- Punch penetrates: Both layers simultaneously
- Each layer receives identical hole at same position
- Hole appears in upper region of folded shape

Step 4 - Unfolding Process:
- Carefully unfold along the vertical crease
- The hole on the right half stays fixed
- The hole on the left half appears as mirror image
- Both holes maintain their vertical position
- Final pattern: Two holes horizontally aligned in the upper portion

Step 5 - Pattern Verification:
- Symmetry check: Holes mirror across vertical center line
- Layer count: 2 layers punched = 2 holes visible
- Alignment: Horizontal alignment at same y-coordinate
- Position: Both in upper portion of paper
- Correct answer: Two holes horizontally aligned in the upper portion

Spatial Reasoning Technique:
Use your finger to trace the fold line vertically. Imagine reflecting the punch point across this line - where your reflection lands is where the second hole appears.

Common Error: Students often confuse the fold direction with the hole alignment direction. Remember: vertical fold → horizontal hole alignment.

Coordinate Method: For hole at (x,y) in folded state, unfolded positions are (x,y) and (100-x,y) for 100x100 paper.