Question

the average age of 15 boys in a class is 11 years. If the 9 years old 5 boys joing the class. then their average will now be---
a)10.33 years c) 10 years
b) 20 years d)10.5 years

Answer 1

10.5 years

Step by step solution:

x / 15 = 11 (Let "x" be the orginal sum of ages before 9 yr. olds were added)

x = 165

165 + 5(9) / 20 = 210 / 20 = 10.5 years old (Since the total sum of all the five 9 year olds and orginal students adds up to 210, we can divide by the total number of students, which is now 20, to find the new average age of the class.

Hope this helped!