This is a sample question on a college test site for math.

2^(5/2)-2^(3/2)

A. 2^(1/2)
B.2
C. 2^(3/2)
D. 2^(5/3)
E.2^2

How do I find know that C is the answer?

Re-express 2^{5/2} as \left( 2^{3/2}\right) \left( 2^{2/2} \right) and then factor out 2^{3/2} from both terms.