I solved it this way:
A is priced at $1, and sold 50 papers of A. Total revenue from selling A is $50.
B is priced at $1.25, and sold 40 papers of B. Total revenue from selling B is $ 50.
Lets assume that the store sold only A and B. Total revenue by selling A and B is $ 100.
That way r is 50%, and p is 500/9.
Then substituted p's value in all the options. D gave back 50% and is the answer.
I used algebra... quite lengthy for a Gmat question... same result as yours...
For A = number of A newspapers sold; similarly for B:
r/100 = A / (A + 1,25B)
p/100 = A / (A + B)
First, one finds A/B for each equation:
A/B = 1,25r / (100 - r)
A/B = p / (100 - p)
Equating both expressions to the right:
r = 400p / (500 - p) => D.
kripalkavi, could you please tell us the origin (Kaplan
, OG, etc) of the question?