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What is the units digit of 1!+3!+5!+7!+9!+11!? 

 Oct 7, 2018
 #1
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Just add up the first two and the rest of them end in zeros:

1! + 3! =1 + 6 =7 - the units digit.

 Oct 7, 2018
 #2
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See, since 5! ends in a zero, all the factorials after that end in a zero! Test it out, yourself. Therefore, 1! ends in 1, and 3! ends in 6. Thus, 1+6+0+0+0+0=7.

 Oct 7, 2018

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