SOLUTION: Find the sum of the multiples of 3 less than 100. Hence or otherwise find the sum of the numbers less than 100 which are not multiples of 3.

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Question 1076650: Find the sum of the multiples of 3 less than 100. Hence or otherwise find the sum of the numbers less than 100 which are not multiples of 3.
Answer by math_helper(2461) About Me  (Show Source):
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3*1 = 3
3*2 = 6
…
3*33 = 99
So there are 33 multiples of 3 less than 100. To find the sum, use +sum%28i%2C+i=1%2Ci=n%29+=+%28n%2A%28n%2B1%29%29%2F2+ and then multiply the result by 3:
3+6+9 +… + 99 = 3(1+2+3+…+33) = +3%2Asum%28i%2C+i=1%2C+i=33%29+=+3%2A%2833%2A34%2F2%29+=+highlight%281683%29+

To find the sum of numbers less than 100 that are not multiples of 3, I would take the approach of finding the sum of all the numbers less than 100 +sum%28i%2C+i=1%2C+i=99%29+=+99%2A100%2F2+ and then subtract from that result, the sum of the multiples of 3 we found above.