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| Quickie XI (Posted on 2017-11-27) |
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What is the last digit in S=sum(n=1 to 99) n!
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Submitted by Ady TZIDON
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Solution:
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Answer:3
Only the 1st four matter:(1+2+6+24) MOD10=3;
from n=5 on all factorials have 0 as the last digit. |
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