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How many four letter words, with or without meaning, can be formed from the letters of ROSE if no letter is repeated?
ATwelve words
BTwenty four
CSixty four
DTwo hundred
Answer & Solution
Correct answer: B. Twenty four
1. All four distinct letters are used, so this is four factorial.
2. The first place has 4 choices, then 3, then 2, then 1.
3. The product 4 times 3 times 2 times 1 gives 24.
_Source: NCERT Class 11 Mathematics, Ch 6 'Permutations and Combinations'_
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