Reading Barron's GRE 19th Edition and came across this quantitative comparison question:
The ratio of red to blue marbles in a jar was 3:5. The same number of red and blue marbles were added to the jar.
Quantity A Quantity B
---------- ----------
the ratio of 3:5
red to blue
marbles now
And the standard quantitative comparison question
A. Quantity A is greater
B. Quantity B is greater
C. Quantities A and B are equal.
D. It is impossible to determine which quantity is greater
The answer it gives is A. It states A) Assume that to start there were $3x$ red marbles and $5x$ blue marbles and that $y$ of each color were added.
Quantity A = Quantity B
$$\frac{3x+y}{5x+y} = \frac{3}{5}$$ $$5(3x+y)=3(5x+y)$$ $$15x+5y=15x+3y$$ $$5y=3y$$ And since $y$ is positive, quantity A must be greater. I do agree with this answer, but that is if $y$ is not equal to 0. But according to the question, it doesn't say you can't add zero marbles to the jar, or is this implied in the question. If it can be, add no marbles to the jar as well, then the answer should be D.