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If s denotes the sum of the integers from 1 to 30 inclusive and t repr
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09 Dec 2021, 02:18
09 Dec 2021, 02:18
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Question Stats:
84% (01:13) correct
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If s denotes the sum of the integers from 1 to 30 inclusive and t represents the sum of the integers from 31 to 60, what is the value of t - s?
(A) 30
(B) 300
(C) 450
(D) 900
(E) Cannot be determined
(A) 30
(B) 300
(C) 450
(D) 900
(E) Cannot be determined
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Joined: 09 Nov 2021
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Affiliations: Private GMAT/GRE Tutor London
Posts: 76
Given Kudos: 6
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
10 Dec 2021, 04:48
1
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.
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.
General Discussion
Re: If s denotes the sum of the integers from 1 to 30 inclusive and t repr
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09 Dec 2021, 19:50
09 Dec 2021, 19:50
1
\(s = 1 + 2 + 3 + ... + 30\)
\(s = \frac{30}{2} (1+30) = 465\)
\(t = 31 + 32 + 33 + ... + 60\)
\(t = \frac{30}{2} (31+60) = 1365\)
\(t - s = 1365 - 465 = 900\)
Answer D
\(s = \frac{30}{2} (1+30) = 465\)
\(t = 31 + 32 + 33 + ... + 60\)
\(t = \frac{30}{2} (31+60) = 1365\)
\(t - s = 1365 - 465 = 900\)
Answer D
