If 15 students in a class average 70% on an exam and 10 students average 90% on the same exam, what is the average in percent for all 25 students?
Choose one
A) 78 %	B) 79 %	C) 80 %	D) 81 %	E) 82 %

Rationale: ( 15 * 70 + 10 * 90 ) / 25 = 78 % the answer is a .
Answer: A