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the sum of first n consecutive positive

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by carefreeamit » Sun Aug 24, 2008 11:10 pm
25 is 13th odd number and 79 is 40th odd number.
sum of odd integers from 25 to 79, inclusive = sum of odd integers till 79 - sum of odd integers till 23 (remember 25 needs to be included in the total)

= 40^2 - 12^2
= 1600 - 144
= 1456
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