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Find the last two digits of the following sum: 5 + 10 + 15 + \cdots + 100.

Apr 30, 2022

#1
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We know that $$100 + 5 = 105$$

We also know that $$50+55 = 105$$

There are 10 cases of this, so the sum is $$10 \times 105 = 1050$$

Can you find the last 2 digits from here?

Apr 30, 2022