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Forty percent of the rats included in an experiment were

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Forty percent of the rats included in an experiment were [#permalink]

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26 Aug 2003, 14:09
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Forty percent of the rats included in an experiment were male rats. If some of the rats died during the experiment and 30 percent of the rats that died were male rats, what was the ratio of the death rate among the male rats to the death rate among the female rats?

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26 Aug 2003, 14:34
As this is GMAT, you really should put answer choices, but...

Let's pick 100 rats to begin with, 40 are male 60 female.
20 die, so 6 male and 14 female die.

so are you looking for the ratio (6/40)/(14/60)
which reduces to (3/20)/7/30), which again reduces to 9/14?
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26 Aug 2003, 18:07
mciatto wrote:
As this is GMAT, you really should put answer choices, but...

Let's pick 100 rats to begin with, 40 are male 60 female.
20 die, so 6 male and 14 female die.

so are you looking for the ratio (6/40)/(14/60)
which reduces to (3/20)/7/30), which again reduces to 9/14?

how did you get the total dead rats as 20 ?

thanks
praetorian
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26 Aug 2003, 20:04
i picked any number that had 30% as a convenient number. You could have picked anything and still come up with the right answer.
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19 Jan 2004, 20:31
out of 100 rats
M = 40 F = 60
Let D be no of dead rats
so MD = 0.3D and FD = 0.7D
Male death rate = 0.3D/40
Female death rate = 0.7D/60

so ratio of male/female death rate = 0.3D/40 * 60/0.7D = 9/14
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20 Jan 2004, 03:55
I have a little different approach. Please note that 30% of the rats that died were male and 70% are female. The male rats that died are30%x40%=12% and for female rats is 60%x70%=42% or 12/40 death rate for male rats and 42/60 death rate for female rats. The desired ratio is 12/40 divided 42/60 which is 12/40x60/42=3/7. ...may be I am wrong since you all get 9/14 as a ratio
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20 Jan 2004, 10:23
Yet another approach (not much different though)

total number of rats = T

So male rates = 0.4T
Female rates = 0.6T

Total rats that died = D

So number of male rats that died = 0.3D
Number of famale rats that died = 0.7D

Death rate for male rats = 0.3D/0.4T

Death rate for female rats = 0.7D/0.6T

The ration = 3D/4T * 7D/6T = 3/4 * 6/7 = 18/28 = 9/14.
20 Jan 2004, 10:23
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