Permutations And Combinations Question 296

Question: How many numbers greater than hundred and divisible by 5 can be made from the digits 3, 4, 5, 6, if no digit is repeated [AMU 1999]

Options:

A) 6

B) 12

C) 24

D) 30

Show Answer

Answer:

Correct Answer: B

Solution:

  • Numbers which are divisible by 5 have ?5? fixed in extreme right place 3 Digit Numbers 4 Digit Numbers H T U Th H T U × × 5 × × × 5 $ ^{3}P_2 $ ways $ ^{3}P_3 $ ways = $ \frac{3!}{1!} $ = $ 3\times 2 $ = $ \frac{3!}{0!} $ = $ 3\times 2 $

$ \Rightarrow $ Total ways = 12.