Abe Got 94 Out of 100 on One Test but Only

Essay

Abe got 94 out of 100 on one test but only 26 out of 50 on a second. He figures he has 94 + 26, or 120, out of 150 and finds that to be 80%. Hence, he cannot understand why his teacher's grade book shows a different result: 94% and 52%, which give an average of $\frac { 94 \% + 52 \% } { 2 }$ = 73%. What accounts for the difference?