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Explain how to calculate 75 + 72 + 69 + 66 + ... + 21 + 18 + 15 + ... + (-66) + (-69) + (-72) + (-75) without a calculator.

 Sep 16, 2022
 #1
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Look at the first and the last numbers

 

Then look at the 2nd and the 2nd last numbers..........what do you see and what do you do?

 Sep 16, 2022

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