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neeti2711: Master | Next Rank: 500 Posts; Posts: 116; Joined: Sat Sep 22, 2012 9:48 pm; Thanked: 3 times

by neeti2711 » Mon Oct 22, 2012 4:59 am

Forty percent of the rats included in an experiment were male rats. If some of the rats died during 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

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Source: Beat The GMAT — Problem Solving | Mon Oct 22, 2012 4:59 am

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Anurag@Gurome: GMAT Instructor; Posts: 3835; Joined: Fri Apr 02, 2010 10:00 pmFollowed by: 523 members; Location: Milpitas, CA; Thanked: 1854 times; GMAT Score:770

by Anurag@Gurome » Mon Oct 22, 2012 5:07 am

neeti2711 wrote:Forty percent of the rats included in an experiment were male rats. If some of the rats died during 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

Algebraic Method:

Total no. of rats = R
No. of rats that died = N

No. of male rats = 40% of R = 0.4R
Death rate of male rats = 0.3N/0.4R
Death rate of female rats = 0.7N/0.6R

Therefore, ratio of the death rate among the male rats to the death rate among the female rats = (0.3N/0.4R)/(0.7N/0.6R) = 18/28 = [spoiler]9/14[/spoiler]

The correct answer is A.

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puneetkhurana2000: Master | Next Rank: 500 Posts; Posts: 131; Joined: Wed Nov 14, 2012 2:01 pmFollowed by: 2 members; Thanked: 39 times

by puneetkhurana2000 » Mon Dec 10, 2012 12:54 pm

Died Not Died Total
Male 0.3x 40
Female 0.7x 60
Total x 100

Let us assume the total number of deaths is x, by given information male deaths is 0.3x and female will be x-0.3x = 0.7x.

There is no need to fill up second columns as we need death rate i.e. (0.3x/40)/(0.7x/60) = 9/14

Hope this helps.

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puneetkhurana2000: Master | Next Rank: 500 Posts; Posts: 131; Joined: Wed Nov 14, 2012 2:01 pmFollowed by: 2 members; Thanked: 39 times

by puneetkhurana2000 » Mon Dec 10, 2012 12:59 pm

Sorry, the table got messed up...the numbers 40, 60 and 100 should be in last column under Total.

And 0.3x, 0.7x and x should be in first column under Died.

Second column is blank as explained in my previous post.

Hope this makes sense!!

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Mon Dec 10, 2012 1:49 pm

neeti2711 wrote:Forty percent of the rats included in an experiment were male rats. If some of the rats died during 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

Let the total number of rats = 100.
Male rats = .4(100) = 40.
Thus, female rats = 100-40 = 60.

Let the total number of deaths = 10.
Male deaths = .3(10) = 3.
Thus, female deaths = 10-3 = 7.

Male death rate = (male deaths)/(total males) = 3/40.
Female death rate = (female deaths)/(total females) = 7/60.
Male death rate / female death rate = (3/40) / (7/60) = 3/40 * 60/7 = 9/14.

The correct answer is A.

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