Permutations and Combinations 1 Question 10

10. The different letters of an alphabet are given. Words with five letters are formed from these given letters. Then, the number of words which have at least one letter repeated, is

(1980, 2M)

(a) 69760

(b) 30240

(c) 99748

(d) None

Analytical & Descriptive Question

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Answer:

Correct Answer: 10. (a)

Solution:

  1. Total number of five letters words formed from ten different letters =10×10×10×10×10=105

Number of five letters words having no repetition

=10×9×8×7×6=30240

Number of words which have at least one letter repeated =10530240=69760



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