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Gmat Prep - Sum of integers question

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by samirpandeyit62 » Sun Oct 28, 2007 6:19 am
The sum of the first 50 positive integers is 2550. What is the sum of the even integers from 100 to 200, inclusive?

this question has been posted many times now

It should beThe sum of the first 50 even positive integers is 2550.

so sum of 100 -200 even integers is

100 + 102 ... 200

100 + 100+2 + 100 +4 + ....100 + 100

= 100*50 + 2+4.....100

= 5000 + 2550 =7550
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Samir
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by gmatguy16 » Mon Oct 29, 2007 3:51 pm
the question says sum of first 50 positive integers, does not say sum of first 50 [b]even[/b] positive integers,something is wrong with the question i guess...
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by samirpandeyit62 » Mon Oct 29, 2007 9:22 pm
Hey gmatguy6 the sum of first 50 positive nos will not be 2550, I've solved this same question before hence I could make out that.
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Samir
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by gmatguy16 » Tue Oct 30, 2007 9:02 am
samir,i am sorry for the confusion ..
i meant the question says sum of first 50 positive integers which means ...1+2+3+4+5 ...=2550 and you have used sum of first 50 even integers as 2550
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by samirpandeyit62 » Tue Oct 30, 2007 10:11 am
Hi gmatguy16,
I've understood ur point man, but just evaluate if it is the sum of first 50 nos i.e 1+2+3.....+50 will it sum upto 2550

sum will be 50*51/2 which will not be 2550

actually this problem was solved some time back on this forum so I just could remember from that question that it was the sum of the first 50 +ve even integers which will be 50*51 = 2550 & solved it accordingly.
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Samir
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by rainbowpo » Thu Apr 24, 2008 6:48 pm
I also think there is something wrong with the original question
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by hillzheng » Sun May 11, 2008 4:30 pm
It is 7550
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by CITI29 » Sun May 11, 2008 8:11 pm
I think the question is correct

sum of 100 -200 even integers is

100 + 102 ... 200

100 + 100+2 + 100 +4 + ....100 + 100

= 100*50 + 2+4.....100
= 100*50 + 2(1+2.....50)
= 5000 + 2*2550
= 5000+ 5100
= 10100

correct answer is C
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