The average weight of students in a class was 60.5 kg. When 8 students, whose average weight was 65 kg, joined the class, the average weight of all the students increased by 0.9 kg. The total number of students now in the class is:
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. 40.
Let the original number of students = x
Total weight before = 60.5x
Weight of 8 students = 8 × 65 = 520
New average = 60.5 + 0.9 = 61.4
Total weight after = 60.5x + 520
New total students = x + 8
= 61.4
⇒ 60.5x + 520 = 61.4x + 491.2
⇒ 520 - 491.2 = 61.4x - 60.5x
⇒ 28.8 = 0.9x
⇒ x = 32
Total students now = x + 8 = 40