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For any positive integer n, the sum of the first n positive

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Manager
Joined: 06 Nov 2008
Posts: 54
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For any positive integer n, the sum of the first n positive [#permalink]  11 Dec 2008, 17:13
For any positive integer n, the sum of the first n positive integers equals [n(n+1)]/2. What is the sum of all the even integers between 99 and 301?

A. 10,100
B. 20,200
C. 22,650
D. 40,200
E. 45,150
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Joined: 29 Aug 2007
Posts: 2497
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Re: sum [#permalink]  11 Dec 2008, 17:27
1
KUDOS
haichao wrote:
For any positive integer n, the sum of the first n positive integers equals [n(n+1)]/2. What is the sum of all the even integers between 99 and 301?

A. 10,100
B. 20,200
C. 22,650
D. 40,200
E. 45,150

Last even integer = 300
First even integer = 100
no. of even integers between 99 and 301 = (300/2 - 100/2) + 1 = 101

sum = no of even integers x average of even integers
sum = 101 (100+300)/2
sum = 101 (200)
sum = 20200
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Manager
Joined: 27 May 2008
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Re: sum [#permalink]  11 Dec 2008, 19:58
GMAT TIGER cool explanation kudos to you +1
Re: sum   [#permalink] 11 Dec 2008, 19:58
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