### Brain Teasers

# Simple Addition 2

What is in the one's digits place in the number that is the sum of 1+2+3+...+999,998+999,999+1,000,000?

### Answer

Zero.Because the sum contains the addition of the following sum in the one's digits place 100,000 times:

0+1+2+3+4+5+6+7+8+9=45

We can deduce that:

100,000 x 45 = 4,500,000

and since 0 is in the one's digits place in this number, we can deduce that 0 is also in the one's digits place in the total sum since only the digits in the one's place can affect the number in the one's digits place.

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