Question

the average age of 16 students is 15 yrs.when a boy of 18 yrs leaves; what will be the average age of remaining 15 students?

Answer 1

Average of 'n' things is $\frac{1}{n}(\Sigma_1^n x_i)$.
Then, average of 16 students = 15 means (sum of ages of al students)/16 = 15.
sum of ages - 18 = 16(15),
new average = 16.

Answer 2

the total puplation is =16*15 which is 240

now that one boy of 18 years left subtract from 240 which is 240-18 =222

now average of 15 students is 222 divide by 15 =14.8

the answer is =14.8