Question 1
What is the rank of the word 'SMART' when all the letters are arranged in dictionary order?
Step-by-Step Solution:
Concept: Rank of a word in dictionary order - counting how many words come before it alphabetically.
Given word: SMART
Strategy:
1. For each position, count arrangements starting with letters smaller than the actual letter
2. Add these counts to find rank
3. The rank is 1 + (number of words before it)
Letters in alphabetical order: A M R S T
Step-by-Step Calculation:
Position 1 (current letter: S):
Available letters: A M R S T
If we place 'A' here: 24 arrangements possible
If we place 'M' here: 24 arrangements possible
If we place 'R' here: 24 arrangements possible
Subtotal arrangements before 'S': 72
Position 2 (current letter: M):
Available letters: A M R T
If we place 'A' here: 6 arrangements possible
Subtotal arrangements before 'M': 6
Position 3 (current letter: A):
Available letters: A R T
Position 4 (current letter: R):
Available letters: R T
Position 5 (current letter: T):
Available letters: T
Final Rank: 79
Verification Strategy:
1. Rank starts at 1 (not 0)
2. We count all words that come alphabetically before our word
3. Our word's rank = 1 + count of words before it
Key Principle:
- At each position, consider all possible smaller letters
- For each smaller letter, count permutations of remaining letters
- Account for repeated letters by dividing by their factorials
General Formula for Position Counting:
At position i, add: Σ (arrangements with smaller letter at position i)
Common Errors:
- Forgetting to start rank from 1
- Not accounting for repeated letters
- Counting arrangements after the word instead of before
Concept: Rank of a word in dictionary order - counting how many words come before it alphabetically.
Given word: SMART
Strategy:
1. For each position, count arrangements starting with letters smaller than the actual letter
2. Add these counts to find rank
3. The rank is 1 + (number of words before it)
Letters in alphabetical order: A M R S T
Step-by-Step Calculation:
Position 1 (current letter: S):
Available letters: A M R S T
If we place 'A' here: 24 arrangements possible
If we place 'M' here: 24 arrangements possible
If we place 'R' here: 24 arrangements possible
Subtotal arrangements before 'S': 72
Position 2 (current letter: M):
Available letters: A M R T
If we place 'A' here: 6 arrangements possible
Subtotal arrangements before 'M': 6
Position 3 (current letter: A):
Available letters: A R T
Position 4 (current letter: R):
Available letters: R T
Position 5 (current letter: T):
Available letters: T
Final Rank: 79
Verification Strategy:
1. Rank starts at 1 (not 0)
2. We count all words that come alphabetically before our word
3. Our word's rank = 1 + count of words before it
Key Principle:
- At each position, consider all possible smaller letters
- For each smaller letter, count permutations of remaining letters
- Account for repeated letters by dividing by their factorials
General Formula for Position Counting:
At position i, add: Σ (arrangements with smaller letter at position i)
Common Errors:
- Forgetting to start rank from 1
- Not accounting for repeated letters
- Counting arrangements after the word instead of before