If a7! + b8! + c9! + d10! = x, where a, b, c and d are natural numbers that are not multiples of 10, then how many distinct values of unit’s digit of x are possible?

Download Number Systems formulas will cover Factorials topic also. 

Hi Hardeep,

It is not clear in the question whether a7! represents a*7! or a7! (like 17! or 27!)

Since the question is a bit ambiguous, we will solve considering both possibilities.

5! is 120.Any factorial greater than that of 5 will end in 0 for sure.

Hence, all the 4 terms must end in 0. The unit digit of X will also be 0. Only 1 distinct value is possible.

You can read about Number system for CAT here.

How is it 9? Can you please tell me?

the answer is 9

1. it would be o.