Problem Solving (PS) | Re: What is 1! + 2! + ... + 10! ?

Notice that the units digit of each answer choice is different; rather than perform the arithmetic as indicated, let’s determine the units digit of each factorial:

1! = 1

2! = 2

3! = 6

4! = 24

After 4!, all other factorials end in zero.

So, the units digit of the answer is 1 + 2 + 6 + 4 = 13, or 3.

Answer: B

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