Problem Solving (PS) | Re: Find unit digit of N when N = 63^1!+2!+...+63! + 18^1!+2!+.

1!+2!+3!+4!...=4k+1

63^1!+2!+...+63! 
63^(4k+1): last digit (3 has a cycle of 3,9,7,1), =3


18^1!+2!+...+18! 
18^(4k+1): last digit (8 has a cycle of 8,4,2,6), =8

37^1!+2!+...37!
37^(4k+1): last digit (7 has a cycle of 7,9,3,1), =7

Unit's digit=3+8+7=18=8

Statistics : Posted by samagra__ • on 12 Sep 2013, 04:19 • Replies 11 • Views 14583

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