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Re: If s denotes the sum of the integers from 1 to 30 inclusive and t repr
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10 Dec 2021, 04:48
Remember that the sum of evenly-spaced numbers can be defined as the average * number of numbers.
For 1 to 30, we see this:
(30+1)/2 * 30 = 31/2 * 30 = 31*15 = (30+1)15 = 450+15 = 465
For 31 to 60, we see:
(31+60)/2 * 30 = 91/2 * 30 = 91*15 = (90+1) * 15 = 1350 + 15 = 1365
The difference, then, is 1365 - 465 = 900.
Answer D.