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Let n=1!+4!+7!.........+400! Then tens digit of n is

Let n=1!+4!+7!.........+400! Then tens digit of n is

Grade:12

1 Answers

Aditya Gupta
2081 Points
5 years ago
unit digit of all factorials after 5 is zero, because p!=5!*6*...*p=120*6*...*p 
now, n is 1+24+10*m.
=25+10*m
so, unit digit is 5.

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