If 18 is 15 percent of 30 percent of a certain number, what : GMAT Problem Solving (PS)
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# If 18 is 15 percent of 30 percent of a certain number, what

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If 18 is 15 percent of 30 percent of a certain number, what [#permalink]

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24 Mar 2013, 11:24
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If 18 is 15 percent of 30 percent of a certain number, what is the number?

(A) 9
(B) 36
(C) 40
(D) 81
(E) 400

Sorry.. i'm quite sure this is a repeat but it's not showing up when i search for it.
[Reveal] Spoiler: OA

Last edited by exploringm on 24 Mar 2013, 13:34, edited 1 time in total.
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Re: if 18 is 15% of 30% of a certain number, what [#permalink]

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24 Mar 2013, 12:29
1
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I'm getting E.

Got the below equation.

18=0.15(0.3*x)

By solving. x = 400.

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Re: if 18 is 15% of 30% of a certain number, what [#permalink]

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24 Mar 2013, 12:33
exploringm wrote:
if 18 is 15 percent of 30 percent of a certain number, what is the number?

(A) 9
(B) 36
(C) 40
(D) 81
(E) 400

Maverick_Indian is right: the answer is E

$$x\frac{15}{100}\frac{30}{100}=18$$

$$x=18*\frac{(100*100)}{(15*30)}$$

$$x=400$$
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Re: if 18 is 15% of 30% of a certain number, what [#permalink]

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24 Mar 2013, 13:29
Maverick_Indian wrote:
I'm getting E.

Got the below equation.

18=0.15(0.3*x)

By solving. x = 400.

My bad guys, E is the official answer. Typed it in too quickly.

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Re: if 18 is 15% of 30% of a certain number, what [#permalink]

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24 Mar 2013, 13:31
Estimate, 18 is 15% (approximately 1/7) 18x7 = 126. Then approximate 30% as 1/3 so 126x3=378, since the answers is so spread answer is E = 400.

I would not use this method is answers is closer to each other.
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Re: If 18 is 15 percent of 30 percent of a certain number, what [#permalink]

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13 Apr 2015, 05:33
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Re: If 18 is 15 percent of 30 percent of a certain number, what [#permalink]

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13 Apr 2015, 18:25
Hi All,

The math involved in this question can be 'set up' (and dealt with) in a variety of ways.

Here, if you're going to take a calculation-based approach, converting the percents to fractions would likely help you speed up (and avoid the last bit of math).

We're told that 18 is 15 percent of 30 percent of a certain number. We're asked for that number.

18 = (.15)(.3)(X)

18 = (3/20)(3/10)(X)

18 = (9/200)(X)

Since 9/200 is a relatively small fraction (it's far less than 10%), we know that 18 is LESS than 10% of X. Based on the given answer choices, there's only one number that is LARGE enough to fit that description....

[Reveal] Spoiler:
E

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Re: If 18 is 15 percent of 30 percent of a certain number, what   [#permalink] 13 Apr 2015, 18:25
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