Question

8
The average of a class of twenty boys is 15 years. If eight boys of 18 years average join the class. Find the new average of the class
2) 17 yrs
3) 20 yrs
1) 15.86 yrs
4) 18.6 yrs​

Answer 1

Given data : The average (age) of a class of twenty boys is 15 years. If eight boys of 18 years average (age) join the class.

To find : Find the new average of the class ?

Solution : Now according to given,

⟹ Average age of 20 boys = Total age of boys/Total boys

⟹ 15 = Total age of boys/20

⟹ Total age of boys = 20 * 15

⟹ Total age of boys = 300 years

∴ Total age of of 20 boys is 300 years.

similarly,

⟹ Average age of 18 boys = Total age of boys/Total boys

⟹ 18 = Total age of boys/8

⟹ Total age of boys = 18 * 8

⟹ Total age of boys = 144 year

∴ Total age of of 8 boys is 144 years.

Total strength of class will be 28 after joining the class by 8 boys.

Now,

⟹ Total age of 28 boys = 300 + 144

⟹ Total age of 28 boys = 444 years

⟹ Average age of 28 boys = Total age of boys/Total boys

⟹ Average age of 28 boys = 444/28

⟹ Average age of 28 boys = 111/7

⟹ Average age of 28 boys = 15.8571

⟹ Average age of 28 boys = 15.86 years (approx)

Answer : The new average age of the class is 15.86 years {Answer : 15.86 years}