Question

If x = 1! + 2! + 3! + 4! + 5! + …. + 2020!
What is first unit digit of x ?

Answer 1

the first unit digit is 3

n! = n × (n - 1) × (n - 2) .... × 3 × 2 × 1

Answer 2

`\boxed{3}`

Explanation:

x = 1! + 2! + 3! + 4! + 5! + ... + 2020!

x = 1 + 2 + 6 + 24 + 120 + 720 + ..0 + 0 +.... + ....0

x = 33 + 120 + ...0 + ...0 + .... + ...0

x = ......3

→ So, the first unit digit of x is 3