#National Science Olympiad Question

19 messages · Page 1 of 1 (latest)

weary blaze
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The sum of 1! + 2! + 3! + .... + 2017! is a number whose digit unit is...

tulip pulsarBOT
weary blaze
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help

solemn schooner
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well... try looking at the last digit of the first few factorials

weary blaze
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1! = 1
2! = 2
3! = 6

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then?

foggy oxide
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1+2+6+4+ a bunch of zeros

weary blaze
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y

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i rlly need an answer

foggy oxide
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what is the last digit of 5! ?
6! ?
7! ?
etc...

hollow linden
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only first 4 factorial values will have an units digit all the other following factorial values will have a 0 in their units digit

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so, the answer for your question is the sum of units digit of 1!+2!+3!+4!

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wiz, 1+2+6+(2)4=13

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so the units digit will be 3

hollow linden
weary blaze
hollow linden
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3 most likely

solemn schooner
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note that for n>=5, n! is always divisible by 10