NDA 2018 Maths · Mathematics · Permutations and Combinations · medium

How many even three-digit numbers can be formed using the digits 1, 2, 3, 4, 5 without repetition?

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Answer: (A) 24

Fix the units digit first, from {2,4}: 2 ways. The hundreds digit then has 4 choices and the tens digit 3 choices. Total

2\times4\times3=24

. Choosing the hundreds digit first would miss the restriction on the last digit.

Original question written in the NDA 2018 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake