Question

The average age of 4 boys, five year ago was
9 years. On including a new boy, the present
average age of all the five is 15 years. The
Present age of new boy is.​

Answer 1

Answer:

age of new boy is 19

Step-by-step explanation:

let age of 5 boys a, b, c, d and e

average age of 4 boys before 5 years is 9

(a-5)+(b-5)+(c-5)+(d-5)/4 = 9

a+b+c+d-20=9×4

a+b+c+d=36+20

a+b+c+d=56

average of 5 boys at present is 15

(a+b+c+d+e)/5= 15

56+e= 15×5

e = 75 - 56

e = 19

age of 5 th boy is 19