in a class, the average age of the students is 17 years. The average age of the boys is 17.4 years while the average age of the girls is 16.8 years. Find the number of girls in the class if there are 21 boys.
Show answer & explanation
Correct answer: D
Explanation
The correct answer is option 4 i.e. 42.
Let the number of girls = G
(21 × 17.4 + G × 16.8)/(21 + G) = 17
⇒ 365.4 + 16.8G = 357 + 17G
⇒ 0.2G = 8.4
⇒ G = 8.4/0.2 = 42