So I'm taking the GRE (Graduate Record Examination) tomorrow and I'm looking over some practice questions. One of them has been driving me crazy.

Stan drove for h hours at a constant rate of r miles per hour. How many miles did he go during the final 20 minutes of his drive?

A. 20r
B. hr/3
C. 3rh
D. hr/20
E. 3r

Isn't the answer r/3???? WTF am i retarded?