The average age of a group of 40 boys is 15 years. A boy aged 20 years leaves the group and a new boy joins. If the average age of the new group becomes 15.2 years, find the age of the new boy.

A20 years

B22 years

C25 years

D28 years ✓ Correct

Correct answer: (D) 28 years

Explanation

The new boy is 28 years old.

total of 40 boys = 40 x 15 = 600.

after the 20 year old leaves = 600 - 20 = 580.

new group total = 40 x 15.2 = 608.

new boy = 608 - 580 = 28 years.

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