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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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New post 29 Aug 2008, 15:33
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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?
(A) 9/14 (B)3/4 (C) 9/11
(D)6/7 (E) 7/8

this looks like a straight forward % question, but i cannot get to the right answer. seems to me that the answers are wrong.
what do you think?

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Re: PS what is wrong with these rats [#permalink]

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New post 29 Aug 2008, 15:43
elmagnifico wrote:
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?
(A) 9/14 (B)3/4 (C) 9/11
(D)6/7 (E) 7/8

this looks like a straight forward % question, but i cannot get to the right answer. seems to me that the answers are wrong.
what do you think?


A

Tm = .4T
Tf = .6T

D = x*T where x is percentage of deaths
Dm = .3*x*T
Df = .7*x*t

DRm = .3xT / .4T = (3/4)x
DRf = .7xT/.6T = (7/6)x

DRm:DRf = 3x/4 : 7x/6 = 18/28 = 9/14

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Re: PS what is wrong with these rats [#permalink]

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New post 30 Aug 2008, 00:17
total no. of rats = R
male = 0.4R
female = 0.6R

total dead rats = D
male = .3D
female = .7D

so death ratio of
male= 0.3D/0.4R AND female = 0.7D/ 0.6R.
let D/R = A

so ratio of male to female = [(0.3/0.4)*A]/ [(0.7/0.6)*A] = 9/14

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Re: PS what is wrong with these rats [#permalink]

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New post 30 Aug 2008, 19:47
Agreed..... 9/14

I solved via a diff. method, by plugging in numbers:

Say there are 100 rats... 40 are M while 60 are F

Next... say, for example, that 20 rats died during testing.
M(death)= .3x20= 6 M deaths
F(death)= .7x20= 14 F deaths

Keeping on.. 6/40 M rats die while 14/60 F rats die

we now have the ratio 6/40 : 14/60 ----> 18/120 : 28/120 ----> 18:28 --> 9/14

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Re: PS what is wrong with these rats   [#permalink] 30 Aug 2008, 19:47
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Forty percent of the rats included in an experiment were

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