The average age of group of 5 friends is 32 years. The youngest friend amongst them is 4 years old. What was the average age of the group at the time of birth of the youngest friend?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 35 years
The youngest friend is 4 years old, so the group is looked at 4 years ago. At that moment the youngest was just born, so the group then had only the other four friends, each 4 years younger than now.
Total age of the 5 friends now \(=5\times32=160\) years
Total age of the other 4 now \(=160-4=156\) years
Their total 4 years ago \(=156-4\times4=140\) years
Average then \(\displaystyle =\frac{140}{4}=35\) years