First slide

Permutations

Question

A code word of length 4 consists two distinct consonants in the English alphabet followed by two digits from 1 to 9, with repetition allowed in digits. If the number of code words so formed ending with an even digit is 432 $k$ , then $k$ is equal to

Moderate

A

5
B

49
C

35
D

7

Solution

.Number of code words ending with even digit
$\begin{array}{l} = (21) (20) (9) (4) \\ ∴ 432 k = (21) (20) (9) (4) \\ \Rightarrow k = 35 . \end{array}$

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