Question

How many 4-digit numbers can be formed by using 2, 4, 6, 8, 10, 12 without repetition of digits?

(a) 15

(b) 42

(c) 70

(d) 127

The question was posed to me in an interview.

I'd like to ask this question from Counting in division Counting of Discrete Mathematics

Answer 1

The correct option is (a) 15

To explain: Here making a 4-digit number is equivalent to filling 4 places with 6 numbers. So, the number of ways of filling all the four places is ^6C4 = 15. Hence, the total possible 4-digit numbers from the above 6 numbers are 15.