150 ml of 30% sulphuric acid was added : GMAT Problem Solving (PS)
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# 150 ml of 30% sulphuric acid was added

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21 Feb 2013, 21:14
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70% (02:31) correct 30% (01:47) wrong based on 127 sessions

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150 ml of 30% sulphuric acid was added to approximate 400 ml of 12% sulphuric acid solution. Find the approximate concentration of the acid in the mixture?

A. 1/2
B. 1/3
C. 1/4
D. 1/6
E. 1/5
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21 Feb 2013, 21:35
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antoxavier wrote:
150 ml of 30% sulphuric acid was added to approximate 400 ml of 12% sulphuric acid solution. Find the approximate concentration of the acid in the mixture?

A. 1/2
B. 1/3
C. 1/4
D. 1/6
E. 1/5

150 ml solution contains 45 ml sulphuric acid
400 ml solution contains 48 ml sulphuric acid
550 ml solution contains 93 ml sulphuric acid

$$\frac{93}{550} \approx \frac{90}{540} = \frac{1}{6}$$

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23 May 2013, 04:03
MacFauz.. Thanks u explained it neatly

The trick is to choose the approximation figures wisely.
I kept trying to approx. 93 to 100 but it still didn't work. Any particular advice on that? How do I decide on reducing/increasing numerator or denominator?
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23 May 2013, 05:05
SaraLotfy wrote:
MacFauz.. Thanks u explained it neatly

The trick is to choose the approximation figures wisely.
I kept trying to approx. 93 to 100 but it still didn't work. Any particular advice on that? How do I decide on reducing/increasing numerator or denominator?

The approximation in this case had to do with realising that a number very close to the denominator is a multiple of a number very close to the numerator.. When you get a complicated looking fraction, that would more often would be the case.... The GMAT does not want you to be doing large calculations...
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04 Oct 2014, 09:43
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19 Apr 2015, 03:18
Do not need any computation

30%-----------21%---------12%

if volume of both sol. were equal the concentration would be 21%=1/5, but 12% is more than 3 times

only possibility is 1/6

D
150 ml of 30% sulphuric acid was added   [#permalink] 19 Apr 2015, 03:18
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