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# ds: r + s

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Director
Joined: 23 May 2008
Posts: 801

Kudos [?]: 83 [0], given: 0

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18 Aug 2008, 14:45
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What is the ratio of r to s?

(1) r + s = 7

(2) r^2 – s^2 = 7

Kudos [?]: 83 [0], given: 0

Director
Joined: 12 Jul 2008
Posts: 514

Kudos [?]: 162 [0], given: 0

Schools: Wharton
Re: ds: r + s [#permalink]

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18 Aug 2008, 14:59
bigtreezl wrote:
What is the ratio of r to s?

C

(1) r + s = 7

(2) r^2 – s^2 = 7

(1) Insufficient

(2) Insufficient

(r+s)(r-s) = 7

(1) and (2)

7*(r-s) = 7
r-s = 1
r+s = 7

1+s+s = 7
s = 3
r = 4

Kudos [?]: 162 [0], given: 0

Director
Joined: 23 May 2008
Posts: 801

Kudos [?]: 83 [0], given: 0

Re: ds: r + s [#permalink]

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18 Aug 2008, 15:08
why cant you deduce from statement B, r^2 - s^2=7, that r is 4 and s is 3 giving an answer of B for the problem

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Intern
Joined: 17 Aug 2008
Posts: 19

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Re: ds: r + s [#permalink]

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18 Aug 2008, 15:18
We don't know if the numbers are positive integers. The second relation will also work if one of the numbers is a negative integer, in which case, there is a different ration. So, C is the best option.

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Re: ds: r + s   [#permalink] 18 Aug 2008, 15:18
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