Question

The tens digit of 1! + 2! + 3! + …+49! Is

• A. 1
• B. 2
• C. 3
• D. 4

Answer 1

Answer: (A)

1

Answer 2

We have 1! + 2! + 3! + 4! = 33. Also 5! = 120, 6! = 720, 7! = 5040, 8! = 40320 and 9! = 326880. Thus, the tens digit of 1! + 2! + … + 9! Is 1.

Also, note that n! is divisible by 100 for all n ≥10, so that tens digits of 10! + 11! + … + 49! is zero. Therefore, tens digit of 1! + 2! +…+49! Is 1