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# Does nm = 40?

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Senior Manager
Joined: 10 Nov 2010
Posts: 262
Location: India
Concentration: Strategy, Operations
GMAT 1: 520 Q42 V19
GMAT 2: 540 Q44 V21
WE: Information Technology (Computer Software)

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01 May 2012, 01:29
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Difficulty:

5% (low)

Question Stats:

94% (01:21) correct 6% (00:25) wrong based on 152 sessions

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Does nm =40?

(1) 10/n = m/4
(2) 5n = 20 and 8m = 80

[Reveal] Spoiler:
a) 10/n = m/4
if we consider different signs of n & m
nm=40 or nm=-40
NS

b) 5n=20 => n=4
8m = 80 =>m=10
=> nm=40 ---Sufficient

Guys do we need to consider that a) is providing ratio so we don't need to consider -ve signs.
[Reveal] Spoiler: OA

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The proof of understanding is the ability to explain it.

Last edited by Bunuel on 12 Jun 2013, 04:53, edited 3 times in total.
Edited the question
Math Expert
Joined: 02 Sep 2009
Posts: 39622
Re: Why we dont need to consider negative values here [#permalink]

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01 May 2012, 01:44
Does nm =40?

(1) $$\frac{10}{n} = \frac{m}{4}$$--> cross multiply $$40=mn$$. Sufficient. So, as you can see we have only one value for $$mn$$

(2) 5n = 20 and 8m = 80 --> $$n=4$$ and $$m=10$$ --> $$mn=40$$. Sufficient.

_________________
Senior Manager
Joined: 10 Nov 2010
Posts: 262
Location: India
Concentration: Strategy, Operations
GMAT 1: 520 Q42 V19
GMAT 2: 540 Q44 V21
WE: Information Technology (Computer Software)
Re: Why we dont need to consider negative values here [#permalink]

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01 May 2012, 05:25
Bunuel wrote:
Does nm =40?

(1) $$\frac{10}{n} = \frac{m}{4}$$--> cross multiply $$40=mn$$. Sufficient. So, as you can see we have only one value for $$mn$$

(2) 5n = 20 and 8m = 80 --> $$n=4$$ and $$m=10$$ --> $$mn=40$$. Sufficient.

Thanks.............
_________________

The proof of understanding is the ability to explain it.

Intern
Joined: 04 Apr 2011
Posts: 10
Schools: Sloan '16
Re: Does nm =40? (1) 10/n = m/4 (2) 5n = 20 and 8m = 80 [#permalink]

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17 Jun 2012, 16:48

At first glance, I thought 10/n = m/4 was not sufficient. Using cross multiplication, I was able to get mn=40. Rephrasing the question, I thought the question needed values for m and n. Not the case for this DS.
Re: Does nm =40? (1) 10/n = m/4 (2) 5n = 20 and 8m = 80   [#permalink] 17 Jun 2012, 16:48
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