In how many different ways can the letters of the word RUMOUR be arranged?
Aptitude
Permutation and Combination
Difficulty: Medium
Choose an option
-
A30
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B90
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C180
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D720
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ENone of these
Answer
Correct Answer: 180
Explanation
### Concept & Formula
When multiple characters are repeated in a word, the total distinct permutations are calculated by dividing the total factorial by the product of the factorials of each character's frequency.
$$P = \frac{n!}{p! \times q!}$$
### Step-by-Step Solution
- **Given:** The word 'RUMOUR'.
- Count the total letters: $n = 6$.
- Identify all duplicates: The letter 'R' appears $2$ times. The letter 'U' appears $2$ times.
- Construct the formula: Total arrangements = $\frac{6!}{2! \times 2!}$.
- Compute the numerator: $6! = 720$.
- Compute the denominator: $2 \times 2 = 4$.
- Divide: $\frac{720}{4} = 180$.
### Exam Strategy & Shortcut
Knowing $6! = 720$, you just need to divide by $4$ since there are two pairs of identical letters. $720 / 4 = 180$.
### Common Pitfall
Failing to spot one of the duplicate pairs (like missing the two 'U's) and dividing only by $2!$, which would give an incorrect answer of $360$.
### Final Answer
Therefore, the correct answer is **180**.