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 newgroup of students increased by 2 kg. How many students are there in the class now?
Answer & explanation
Correct answer: option 2
10 students join the group ,
Sum of weight of 10 students = 10 × 68 = 680 kg
6 students leave the group ,
Sum of weight of 6 students = 6 × 60 = 360 kg
Difference in weight = 680 - 360 = 320 kg
Let initial number of person = N
According to question ,
N × 69.5 + 320 = ( N + 4 ) × 71.5
69.5N + 320 = 71.5N + 286
2N = 34
N = 17
So , Number of students in class now = N + 4 = 17 + 4 = 21