In a hostel, the average age of 30 students was 18 years. Later, 5 students left and 5 new students joined. The average age of the new group became 17.2 years. If the average age of the 5 students who left was 20.4 years, find the average age of the 5 students who joined.
Show answer & explanation
Correct answer: B
Explanation
Given:
Initial number of students = 30
Initial average age = 18 years
New average = 17.2 years
Average age of the 5 students who left = 20.4 years
Formula:
Total age = Average × Number
Initial total age = 30 × 18 = 540
Total age of the 5 students who left = 5 × 20.4 = 102
Age of the remaining 25 students = 540 − 102 = 438
Total age of the new group = 30 × 17.2 = 516
Total age of the 5 new students = 516 − 438 = 78
Their average age = 78 / 5 = 15.6 years