+0  
 
0
52
2
avatar

what is the units digit sum of 1! + 2! + 3! + .....+n! when n = 2019?

 Dec 14, 2018

Best Answer 

 #1
avatar+3729 
+2

Notice that after 5! every number will end in 0. So, we are just looking for 1!+2!+3!+4! which ends in a 3. 

 Dec 14, 2018
 #1
avatar+3729 
+2
Best Answer

Notice that after 5! every number will end in 0. So, we are just looking for 1!+2!+3!+4! which ends in a 3. 

tertre Dec 14, 2018
 #2
avatar+731 
0

In 5! and up, there is a 2 and a 5, and when multiplied, they equal 10, which has a 0 in the units digit.

PartialMathematician  Dec 15, 2018

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