Now write an equation that says that the expressions for the two volumes are equal to each other,
and solve for r:
The answer is (B).
PICK NUMBERS
When the answer choices are algebraic expressions, it is often quickest to pick numbers for
the unknowns, plug those numbers into the stem and see what you get, and then plug those
same numbers into the answer choices to find matches.Warning: When you pick numbers, you have to check all the answer choices. Sometimes
more than one works with the number(s) you pick, in which case you have to pick numbers
again.So the direct way to do this question is the algebraic way. But as you can see, the algebra is quite
convoluted, and the matter of the different r’s can be confusing. There’s another way to do this
question: Pick Numbers. All the given measures are in terms of x, and all the answer choices are in
terms of x, so to make things simpler, you could just pick a number for x, plug it into the question,
and see what you get. Pick a number that’s easy to work with.