Multiple choice

The average weight of some students in a class was 69.5 kg. When 10 students of average weight 68 kg joined the class, and 6 students of average weight 60 kg left the class, it was noted that the average weight of the new group of students increased by 2 kg. How many students are there in the class now?

  1. 19

  2. 21

  3. 23

  4. 17

  5. None of these

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let n be original students with total weight 69.5n. After 10 students (total 680kg) join and 6 students (total 360kg) leave: new total = 69.5n + 680 - 360 = 69.5n + 320, new count = n + 4. New average = (69.5n + 320)/(n + 4) = 71.5. Solving: 69.5n + 320 = 71.5n + 286, so 34 = 2n, n = 17. Current students = 17 + 4 = 21.