The average (arithmetic mean) of 16 students first quiz scores in a difficult English class is 61.5. When one student dropped the class, the average of the remaining scores increased to 64.0. What is the quiz score of the student who dropped the class? Choose the correct choice from the following answers
A) 10 B) 24 C) 40 D) 55 E) 70

Rationale: "total score of 16 students is 16 * 61.50 = 984 total score of 15 students is 15 * 64 = 960 so , the score of the person who left is 24 ( 984 - 960 ) answer will be ( b )"
Answer: B