Question

The mean weight of 21 students is 21 kg. If a student weighing 21 kg is removed from the group,
then the mean of of the remaining students is

(a) 20 kg (b) 21 kg (c) 19 kg (d) 18 kg

Answer 1

Mean weight = 21 kg
Number of students = 21
Sum of weights of 21 students = 21 $\text{×}$ 21 = 441
Sum of weights of 20 students left = 441 − 21 = 420
Mean of remaining students = $\frac{420}{20}=21\mathrm{kg}$
Hence, the correct option is (b).