Permutations And Combinations Question 168

Question: The number of words of four letters containing equal number of vowels and consonants, where repetition is allowed, is

Options:

A) $ 105^{5} $

B) $ 210\times 243 $

C) $ 105\times 243 $

D) $ 150\times 21^{2} $

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Answer:

Correct Answer: D

Solution:

  • [d] Let us first select two places for vowel, which can be selected from 4 places in $ ^{4}C_2 $ ways. Now this places can be filled by vowels in $ 5\times 5=25 $ ways as repletion is allowed. The remaining two places can be filled by consonants in $ 21\times 21 $ ways. Then the total number of words is $ ^{4}C_2\times 25\times 21^{2}=150\times 21^{2} $ .