confusing DS!

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rahi08: Newbie | Next Rank: 10 Posts; Posts: 6; Joined: Tue Feb 26, 2008 5:04 pm

by rahi08 » Thu Sep 25, 2008 1:23 pm

Value of (a+b)?
1- a^2+b^2=13
2- 2b=12/a
Answer: C ?
I think it shoud be E because we get to answer for a+b
could somebody help?

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Source: Beat The GMAT — Data Sufficiency | Thu Sep 25, 2008 1:23 pm

Morgoth: Master | Next Rank: 500 Posts; Posts: 316; Joined: Mon Sep 22, 2008 12:04 amFollowed by: 1 member; Thanked: 36 times

Re: confusing DS!

by Morgoth » Thu Sep 25, 2008 1:40 pm

rahi08 wrote:Value of (a+b)?
1- a^2+b^2=13
2- 2b=12/a
Answer: C ?
I think it shoud be E because we get to answer for a+b
could somebody help?

2b=12/a
ab = 6

a^2+b^2=13
a^2 + b^2 + 2ab = 13+2ab
(a+b)^2 = 13+12
(a+b)^2 = 25
(a+b) = 5

Now here I am little confused about the whole thing
if
(a+b)^2 = 25
then,
a+b = -5
or
a+b = 5
Can someone pls guide me on this. This thing keeps troubling me for some or the other reason.

When to consider both + and - for squares.

Thanks.

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ddm: Master | Next Rank: 500 Posts; Posts: 162; Joined: Mon Jul 28, 2008 8:33 pm; Location: San Jose,CA; Thanked: 1 times

by ddm » Thu Sep 25, 2008 6:07 pm

Same question as morgoth.

A+B=5 OR -5

Answer should be E?

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