SOLUTION: Find the sum of all the positive integers less than 100 that are multiples of 3.

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Question 983880: Find the sum of all the positive integers less than 100 that are multiples of 3.
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The numbers are:
3, 6, 9, 12, 15 . . . 99
I can express the sum as:
1*3 +2*3 + 3*3 + 4*3 + 5*3 + . . . + 33*3
Also as:
3*( 1 + 2 + 3 + 4 + 5 + . . . + 33 )
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The formula for the sum of numbers from
1 to n is: +S+=+%281%2F2%29%2A%28+n%2A%28+n%2B1+%29%29+
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for instance:
+1+%2B+2+%2B+3+%2B+4+%2B5+=+15+
+S+=+%281%2F2%29%2A%28+5%2A6+%29+
+S+=+15+
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3*( 1 + 2 + 3 + 4 + 5 + . . . + 33 ) = +3%2A%281%2F2%29%2A%28+33%2A34+%29+
+S+=+%28+3%2F2%29%2A1122+
+S+=+3%2A561+
+S+=+1683+
Hope I got it!