The ratio of the number of boys to that of girls in a class is 4 : 5. The average score in mathematics of all the boys and girls is 70. If the average score of the girls is 30% more than that of the boys, then what is the average score of the boys?
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 60.
Let boys' average = B
(4 × B + 5 × 1.3B)/(4 + 5) = 70
⇒ (4B + 6.5B)/9 = 70
⇒ 10.5B/9 = 70
⇒ B = (70 × 9)/10.5 = 60