The average age of a group of 25 boys is 17 years. If one boy...

Given: The average age of a group of 25 boys is 17 years. If one boy leaves the group, the average age becomes 17.2 years. We need to find the age of the boy who left the group. Solution: Calculate the total age of all 25 boys. Average age of 25 boys $=17$ years Total age of 25 boys (=25 \times 17=425) years Calculate the total age of 24 boys after one leaves. New average age of 24 boys $=17.2$ years Total age of 24 boys (=24 \times 17.2=412.8) years Find the age of the boy who left the group. Age of the boy who left $=$ Total age of 25 boys - Total age of 24 boys Age of the boy who left $=425-412.8=12.2$ years Conclusion: The age of the boy who left the group is $12.2$ years.