Question

The digit in the unit’s place of 7171 + (177)! is

Answer 1

any number  which is  n !    for  n >= 5  will have  10 as one of its factors...

5!  = 5 * 4 * 3 * 2 * 1 = 4 * 3 * 5*2 =  4* 3 * 10

so 177 !    will have  0 at the units place.

7171 + 177 !    will have   1 at the units place. 

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10!  has  two zeros at the end.
15!  has to have 3 zeros at the end.
20!  has to have 4 zeros  at the end.
25!  has to have 6 zeros at the end, as  25 = 5 * 5,  there are two 5s.
30 !  has 7 zeros.
35!
40!  has  9 zeros.
50!  has  12 zeros,  as  50 = 5 * 5 * 10