The average age of 6 brothers is 15 years. The age of the youngest brother is 5 years. What was the average age (in years) of the group of brothers at the time of birth of the youngest brother?
- A14
- B15
- C12.5
- D12
Solution & Step-by-step Explanation
Number of brothers = 6
Current average age = 15 years
Current total age = 6×15=90 years
The youngest brother is 5 years old. The time of his birth was 5 years ago.
To find the total age of the brothers 5 years ago, we subtract 5 years from the age of each of the 6 brothers:
Total age 5 years ago=90−(6×5)=90−30=60 years
At the time of birth of the youngest brother, he was just born (age = 0). The group at that instant consisted of the remaining 5 older brothers if excluding him, or 5 brothers contributing to the active age divisor. Standard competitive exam interpretation computes the average of the remaining 5 brothers:
Average age=
5
60
=12 years
Current average age = 15 years
Current total age = 6×15=90 years
The youngest brother is 5 years old. The time of his birth was 5 years ago.
To find the total age of the brothers 5 years ago, we subtract 5 years from the age of each of the 6 brothers:
Total age 5 years ago=90−(6×5)=90−30=60 years
At the time of birth of the youngest brother, he was just born (age = 0). The group at that instant consisted of the remaining 5 older brothers if excluding him, or 5 brothers contributing to the active age divisor. Standard competitive exam interpretation computes the average of the remaining 5 brothers:
Average age=
5
60
=12 years