how to deal with this GMAT math question?

Submitted by GMAT800 on Sat, 10/08/2011 - 15:12

On two of his tests, Harry scored 30 out of a maximum of 50 and on the third he scored 40 out of a maximum of 100? What is his average percentage score on the three tests?

 

(a) 33.33%
(b) 40%
(c) 50%
(d) 53.3%
(e) 66.66%