If 15 students in a class average 70% on an exam and 10 students average 95% on the same exam, what is the average in percent for all 25 students? Choose the correct answer:
A) 77 %  B) 78 %  C) 79 %  D) 80 %  E) 81 %

Rationale: "( 15 * 70 + 10 * 95 ) / 25 = 80 % the answer is d ."
Answer: D