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Multiplication Problem

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Multiplication Problem

by student22 » Fri Mar 12, 2010 12:56 pm
(0.025 * 15/2 * 48) / (5 * 0.0024 * 3/4) =

A. 0.1
B. 0.2
C. 100
D. 200
E. 1,000
E

Is there a number properties or logical reasoning way to quickly solve this problem? Otherwise, you'd have to be rain man to solve it in less than 2 minutes using straight multiplication. [/quote]
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by papgust » Fri Mar 12, 2010 6:26 pm
(25/1000 * 15/2 * 48) / (5 * 24/10000 * 3/4)

Take reciprocal of denominator,

25/1000 * 15/2 * 48 * 1/5 * 10000/24 * 4/3

Cancelling, you get

25 * 4 * 10 = [spoiler]1000 (E)[/spoiler]
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by Stuart@KaplanGMAT » Fri Mar 12, 2010 11:46 pm
When the answer choices are so spread out, we can also estimate to find the right answer:

(0.025 * 15/2 * 48) / (5 * 0.0024 * 3/4)

let's rearrange it to:

0.025/0.0024 * (15/2)/5 * 48/(3/4)

estimating, we have:

more than 10 * more than 1 * more than 48 = more than 480... choose E.
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by Phirozz » Sat Mar 13, 2010 12:08 am
student22 wrote:
(0.025 * 15/2 * 48) / (5 * 0.0024 * 3/4) =

A. 0.1
B. 0.2
C. 100
D. 200
E. 1,000
E

Is there a number properties or logical reasoning way to quickly solve this problem? Otherwise, you'd have to be rain man to solve it in less than 2 minutes using straight multiplication.
[/quote]

Cancal 15/2 from both numarator and denomator. Now we are geting (0.025*48)/0.0012. Now 0.0025/0.0012 is definitely more than 20 so result is more than 20*48 ie 960. Answer is E
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by student22 » Sat Mar 13, 2010 12:53 pm
Just had a chance to get back to this topic. Thanks guys, this is exactly what I was looking for, since the GMAT wouldn't put a question that you had to spend 3 minutes on to solve.
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