Solutions
1! = 1 = is not divisible by 8
2! = 2x1 = is not divisible by 8.
3! = 3x2x1 = is not divisible by 8.
4! = 4x3x2x1 = is divisible by 8.
Similarly, 5!, 6!, 7!, ,,,,, 100! are all divisible by 8
Since 4!, 5!, 6!, 7!, ,,,,, 100! all are divisible by 8, we can write it their sum as 8x
Now ,
1! + 2! + 3! + 8(x)
= 1 + 2 + 6 + 8(x)
= 8x + 8 + 1
so, on dividing the above equation by 8,we get remainder = 1