1.

Find the last digit of the sum of 1!+2!+........+49!

Answer»

1!+2!+3!......+49!=
in between this there is 5! and after that EVERY numbers factorial has unit digit 0...
so,1!=1
2!=1*2=2
3!=1*2*3=6
4!=1*2*3*4=24
5!=1*2*3*4*5=120
.......
.........
so, 1+2+6+24+120+720......
unit digit=1+2+6+...4=13
last digit=3

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