In a class, the average age of 15 boys is 11 years. If 5 boys, each aged 9 years, join them, what is the new average age?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 10.5 years
The average of a combined group is the total of all the ages divided by the total number of boys.
Total age of the 15 boys \(=15\times11=165\) years
Total age of the 5 new boys \(=5\times9=45\) years
Total age of all 20 boys \(=165+45=210\) years
New average \(\displaystyle =\frac{210}{20}=10.5\) years
The new average age is 10.5 years.