Squares Rectangular

Rectangular Grid Square Counting problems involve counting squares in an m×n grid (where m and n may be different). The number of squares is limited by the smaller dimension, and the formula sums over square sizes from 1 to min(m,n).

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200+Practice Questions
IntermediateDifficulty
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Introduction to Squares Rectangular

Rectangular Grid Square Counting problems involve counting squares in an m×n grid (where m and n may be different). The number of squares is limited by the smaller dimension, and the formula sums over square sizes from 1 to min(m,n).

Prerequisites

Understanding of grid structure Summation formulas Knowledge that square size limited by smaller dimension Basic arithmetic
Why This Matters: Rectangular Grid problems appear in 1-2 questions in SSC CGL and Banking PO exams. They test application of combinatorial formulas.

How to Solve Squares Rectangular Problems

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Step 1: Identify grid dimensions: rows = m, columns = n (assume m ≥ n for convenience)

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Step 2: The largest possible square size is n (the smaller dimension)

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Step 3: For k×k squares, number = (m - k + 1) × (n - k + 1)

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Step 4: Sum for k = 1 to n: Total = Σ (m - k + 1)(n - k + 1)

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Step 5: Simplify: Let a = m+1, b = n+1, then total = Σ (a - k)(b - k) for k=1 to n

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Step 6: Use formula: Total = m×n + (m-1)(n-1) + (m-2)(n-2) + ... + (m-n+1)×1

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Step 7: Calculate the sum

Pro Strategy: Always orient the grid so that m ≥ n (larger dimension first). The number of k×k squares is (m - k + 1)(n - k + 1). Sum from k=1 to n to get total squares.

Example Problem

Example: Count total squares in a 2×3 grid (2 rows, 3 columns). Solution: Step 1: m = 3 (columns), n = 2 (rows) - let's take m≥n, so m=3, n=2 Step 2: k=1 (1×1 squares): (3-1+1)×(2-1+1) = 3×2 = 6 Step 3: k=2 (2×2 squares): (3-2+1)×(2-2+1) = 2×1 = 2 Step 4: Total = 6 + 2 = 8 Answer: 8 squares

Pro Tips & Tricks

  • For m×n grid with m≥n: Total squares = Σ_{k=1 to n} (m - k + 1)(n - k + 1)
  • For 2×3 grid: 6 (1×1) + 2 (2×2) = 8
  • For 2×4 grid: 8 (1×1) + 3 (2×2) = 11
  • For 3×4 grid: 12 (1×1) + 6 (2×2) + 2 (3×3) = 20
  • For 3×5 grid: 15 + 8 + 3 = 26
  • The maximum square size is min(m,n)

Shortcut Methods to Solve Faster

Total squares = Σ (m - k + 1)(n - k + 1) for k=1 to min(m,n)
For 2×n grid: Total = 2n + (n-1) = 3n - 1? Check: 2×3→6+2=8, 3n-1=8 ✓
For 3×n grid with n≥3: Total = 3n + 2(n-1) + 1(n-2) = 6n - 4? Check 3×4→12+6+2=20, 6×4-4=20 ✓

Common Mistakes to Avoid

Using square grid formula (sum of squares) for rectangular grid
Counting squares larger than the smaller dimension
Forgetting that (m-k+1)(n-k+1) counts all positions for k×k squares
Not taking m ≥ n before calculation

Exam Importance

Squares Rectangular is an important topic for various competitive exams. Here's how frequently it appears:

SSC CGL
1-2 questions
BANKING PO
1-2 questions
RAILWAYS RRB
1-2 questions
CAT
0-1 questions
INSURANCE
1-2 questions

Ready to Master Squares Rectangular?

Start with Worksheet 1 and work your way up to expert level! Each worksheet includes:

20 practice questions
Detailed solutions
Step-by-step explanations
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