apollo168 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 storeâ€™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 â€“ p)

B. 150p / (250 â€“ p)

C. 300p / (375 â€“ p)

D. 400p / (500 â€“ p)

E. 500p / (625 â€“ p)

Ans D had to plug in values to get the answer. Couldnt arrive at the answer algebraically within the 2 minute mark

This is fairly straightforward:

total revenue = a(1.00) + b(1.25)

where a and b are the number of newspapers of type A and B that were sold

now r% = a/(a+1.25b)

simplifying:

b = a/1.25 *(100 - r)/r --- (eq 1)

Additionally we have:

p% = a/(a+b)

Simplying and collecting terms of b:

b = a/p (100 - p ) --- (eq 2)

from 1 and 2,

1/p (100-p) = 0.8(100-r)/r

Simplify and collect terms of p on right side:

1000r - 10rp = 800p - 8rp

r(1000-2p) = 800p

therefore: r = 400p/(500-p) Ans: D