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Jacob’s little brother bragged that he could add all numbers from from 1 to 10 (55).Not to be outdone, Jacob said he could add all numbers from 1 to 100 (the answer is 5050).Perhaps because Jacob was a bit too smuck about it, Jacob’s little brother gave him a challenge — can you add all numbers from 1 to 99, but excluding all multiples of2 or 5? In other words,1 + 3 + 7 + 9 + 11 + 13 + 17 + 19 + 21 + 23 + 27 + 29 +...To make sure Jacob doesn’t just randomly give an answer, the little brother is askingyoufor the correct answer (he’s one smart cookie), so what is it?

 Feb 7, 2021
 #1
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The sum is 2200.

 Feb 8, 2021
 #2
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Answer

= (1 + 2 + 3 + ... + 99) - (2 + 4 + 6 + 8 + 10 + ... + 98) - (5 + 10 + 15 + 20 + ... + 95) + (10 + 20 + ... + 90)

= 4950 - 2450 - 950 + 450

= 2000

 Feb 8, 2021

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