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700+ problem

by deepak123gmat » Thu Oct 07, 2010 12:23 am
Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of
Newspaper B for $1.25 each, and the store sold no other newspapers that day. If r
percent of the store's revenues from newspaper sales was from Newspaper A and if p
percent of the newspapers that the store sold were copies of newspaper A, which of the
following expresses r in terms of p?

A. 100p / (125 - p)
B. 150p / (250 - p)
C. 300p / (375 - p)
D. 400p / (500 - p)
E. 500p / (625 - p)

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by pkan51 » Thu Oct 07, 2010 1:08 am
Yeah please someone help this guy and me out. Can't link the answers and the given information together -_-

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by yuliawati » Thu Oct 07, 2010 1:46 am
I think the answer is D.

1. We need to calculate the total revenue (R).
R= (Price of newspaper A*Number of sold of Newspaper A)+(Price of newspaper B*Number of sold of Newspaper B)

= (1*P) + (1.25* (100-p)) -----> note: if p% of the newspapers that the store sold were copies of newspaper A, then (100-p)% of the newspapers that the store sold were newspaper B.

= P + 125 + 1.25P

= 125 - 0.25P

R% of total revenue was from newspaper A, we can rewrite it as:

r/100 = p/(125-0.25p)
r = 100p/(125-0.25p)
To get the answer, we need to multiply the result by 4, we get 400p/(500-p) --> (D).

Hope this help.

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by nileshpadwal » Thu Oct 07, 2010 3:35 am
Answer is D.

Plug in the numbers

Let total number of newspapers sold=100 no. of A=60 no. of B=40 so p=60
Then Revenue from each A=60*1=60$ and B=40*1.25=50
So r= (60/110)*100=600/11

now Plug in p=60

400*60/(500-60)=400*60/440=(600/11)=r
hence D.

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by GMATGuruNY » Thu Oct 07, 2010 5:15 am
deepak123gmat wrote:Last Sunday a certain store sold copies of Newspaper A for $1.00 each and copies of
Newspaper B for $1.25 each, and the store sold no other newspapers that day. If r
percent of the store's revenues from newspaper sales was from Newspaper A and if p
percent of the newspapers that the store sold were copies of newspaper A, which of the
following expresses r in terms of p?

A. 100p / (125 - p)
B. 150p / (250 - p)
C. 300p / (375 - p)
D. 400p / (500 - p)
E. 500p / (625 - p)
I too would plug in numbers. I would use smaller numbers to make the math a bit easier.

1 copy of A sold = $1
4 copies of B sold = 4*1.25 = $5
Total sold = 1+4 = 5.
p = 1/5*100 = 20
Total revenue = 1+5 = 6.
r = 1/6*100 = 50/3. This is our target answer.

Now we plug p=20 into all the answers to see which gives us our target of 50/3.

Only answer choice D works:
(400*20)/(500-20) = 8000/480 = 50/3.

The correct answer is D.
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by deepak123gmat » Thu Oct 07, 2010 5:16 am
Thank you all.
correct ans is D.