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GMAT Avengers Study Group Practice Question - Ratio

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GMAT Avengers Study Group Practice Question - Ratio

by helen.xia@mbawatch » Sun Sep 22, 2013 9:42 am
FOR GMAT AVENGERS STUDY GROUP PARTICIPANTS - NO EXPERT REPLIES NEEDED

If ½ of the number of white mice in a certain laboratory is 1/8 of the total number of mice, and 1/3 of the number of gray mice is 1/9 of the total number of mice, then what is the ratio of the number of white mice to the number of gray mice?

a) 2:3
b) 3:4
c) 4:5
d) 8:9
e) 16:27
Last edited by helen.xia@mbawatch on Sun Sep 22, 2013 9:54 am, edited 1 time in total.
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by theCodeToGMAT » Sun Sep 22, 2013 9:51 am
N = Total number of mice
W = White Mice
G = Gray mice

1/2 W = 1/8 N
N = 4 W

1/3 G = 1/9 N
N = 3 G

W/G = (N/4)/(N/3) = 3/4

Are you sure of the Answer choices????

I guess you mistakenly wrote {B} as 2:4 rather than 3:4... as 2:4 should have been written 1:2
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by helen.xia@mbawatch » Sun Sep 22, 2013 10:00 am
Thank you theCodeToGMAT for spotting the error!
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by GMATGuruNY » Sun Sep 22, 2013 10:12 am
helen.xia@mbawatch wrote:If ½ of the number of white mice in a certain laboratory is 1/8 of the total number of mice, and 1/3 of the number of gray mice is 1/9 of the total number of mice, then what is the ratio of the number of white mice to the number of gray mice?

a) 2:3
b) 3:4
c) 4:5
d) 8:9
e) 16:27
Let the total number of mice = the LCM of 8 and 9 = 72.

½ of the number of white mice in a certain laboratory is 1/8 of the total number of mice.
Since 1/8 * 72 = 9, and this value is 1/2 the number of white mice, the number of white mice = 18.

1/3 of the number of gray mice is 1/9 of the total number of mice.
Since 1/9 * 72 = 8, and this value is 1/3 the number of gray mice, the number of gray mice = 24.

Thus:
white mice : gray mice = 18:24 = 3:4.

The correct answer is B.
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by ganeshrkamath » Tue Sep 24, 2013 1:07 am
helen.xia@mbawatch wrote:FOR GMAT AVENGERS STUDY GROUP PARTICIPANTS - NO EXPERT REPLIES NEEDED

If ½ of the number of white mice in a certain laboratory is 1/8 of the total number of mice, and 1/3 of the number of gray mice is 1/9 of the total number of mice, then what is the ratio of the number of white mice to the number of gray mice?

a) 2:3
b) 3:4
c) 4:5
d) 8:9
e) 16:27
W/2 = T/8 => W = T/4
G/3 = T/9 => G = T/3

W/G = (T/4)/(T/3) = 3/4

Choose b

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