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# Does nm = 40?

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Manager
Joined: 10 Nov 2010
Posts: 223
Location: India
Concentration: Strategy, Operations
GMAT 1: 520 Q42 V19
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WE: Information Technology (Computer Software)

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Updated on: 12 Jun 2013, 04:53
1
00:00

Difficulty:

5% (low)

Question Stats:

92% (00:22) correct 8% (00:37) wrong based on 221 sessions

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Does nm =40?

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

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.

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The proof of understanding is the ability to explain it.

Originally posted by GMATD11 on 01 May 2012, 01:29.
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: 46207
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.

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Manager
Joined: 10 Nov 2010
Posts: 223
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.............
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The proof of understanding is the ability to explain it.

Intern
Joined: 04 Apr 2011
Posts: 9
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.
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Re: Does nm = 40? [#permalink]

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23 Sep 2017, 22:19
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Re: Does nm = 40?   [#permalink] 23 Sep 2017, 22:19
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