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If S is the sum of the first n positive integers, what is

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Manager
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If S is the sum of the first n positive integers, what is [#permalink] New post 02 May 2006, 03:56
If S is the sum of the first n positive integers, what is the value of n ?

(1) S < 20
(2) s^2 > 220

Please explain the anwser.
SVP
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 [#permalink] New post 02 May 2006, 04:29
I think it's (E):

(1) is not suffisient
(2) is not suffisient

(1) and (2) :
> 15 passes the limit of S^2 > 220
> 16 also
> 17 also ...
> 19

after that u have to sum n intergers to obtain 15 or 16 or 17 ... That is obviously possible by many ways :)

For both these reasons, it's (E)
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 [#permalink] New post 02 May 2006, 05:41
Answer is E

1. n could be 2,3,4,5
2. n could be 2,3,4
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 [#permalink] New post 02 May 2006, 06:40
From (1):

n could be 1, 2, 3, 4 or 5.

From (2)

n > 4 (at least n=5 with S=225).

Therefore, the only overlapping value is n=5.

So C.
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 [#permalink] New post 02 May 2006, 12:15
oops

It is C

I read S^2 > 220 as S^2 < 220
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 [#permalink] New post 03 May 2006, 03:07
I see my mistake.... *first* positive integers :)

I agree on C
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 [#permalink] New post 03 May 2006, 03:14
Yeah often I also make the same mistake!!
  [#permalink] 03 May 2006, 03:14
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