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What is the sum of all the integers from 1 to 80, inclusive?
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30 Aug 2018, 07:51
30 Aug 2018, 07:51
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Question Stats:
88% (00:34) correct
11% (01:22) wrong based on 72 sessions
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What is the sum of all the integers from 1 to 80, inclusive?
(A) 3,200
(B) 3,210
(C) 3,230
(D) 3,240
(E) 3,450
(A) 3,200
(B) 3,210
(C) 3,230
(D) 3,240
(E) 3,450
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Joined: 10 Apr 2015
Posts: 6218
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Re: What is the sum of all the integers from 1 to 80, inclusive?
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30 Aug 2018, 10:07
30 Aug 2018, 10:07
sandy wrote:
What is the sum of all the integers from 1 to 80, inclusive?
(A) 3,200
(B) 3,210
(C) 3,230
(D) 3,240
(E) 3,450
(A) 3,200
(B) 3,210
(C) 3,230
(D) 3,240
(E) 3,450
Useful formula: 1 + 2 + 3 + 4 + . . . + n = (n)(n + 1)/2
For example, 1 + 2 + 3 + 4 + . . . + 10 = (10)(10 + 1)/2 = 55
So, 1 + 2 + 3 + 4 + . . . + 80 = (80)(80 + 1)/2
= (80)(81)/2
= (40)(81)
= 3240
Answer: D
Cheers,
Brent
Re: What is the sum of all the integers from 1 to 80, inclusive?
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31 Aug 2018, 21:54
31 Aug 2018, 21:54
We can use A.P too,
sum = n(2a+(n-1)d)/2
= 80(2+79)/2
= 40*81=3240
sum = n(2a+(n-1)d)/2
= 80(2+79)/2
= 40*81=3240
