Question
Tue February 12, 2013 By:
 

1!+2!+3!.......+49! is divided by 20 whats remain

Expert Reply
Tue February 12, 2013
We have:
5! = 120 = 0(mod 20)
6! = 0(mod 20)
....
49! = 0(mod 20)
 
Therefore,
1!+2!+3!+4!+...+49! = 1+2+6+24 (mod 20) = 33 (mod 20) = 13 (mod 20)
 
Hence, the remainder = 13
 
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