Math CentralQuandaries & Queries


Question from Emily, a student:

What is the tens digit in the sum 7! + 8! + 9! ... + 2006!

I know there's an easy way to figure it out but i just can't remember.

Hi Emily.

Any of these terms over 10! is a multiply of 10!, right?

And 10! has the factors 10, 5, and 2 (and the others).

What does that tell you?

Stephen La Rocque.


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