Correct Answer - Option 4 : 12
Given:
The average age of 6 brothers = 15 years
The age of youngest brother = 5 years
Formula used:
Average = sum of the ages/number of persons
Calculations:
Sum of the 6 persons = 6 × 15
⇒ 90
When the youngest brother born the sum of the remaining 6 brothers = 90 - 6 × 5
⇒ 90 - 30 = 60
Average of the group of brothers when the younger one born = 60/5
⇒ 12 years
∴ The average age of 6 members when younger one born is 12 years
At the time of birth, the age of the newly born baby is 0
So, the average age of 6 boys = 60/6 = 10 years
But here, no such option is available in the official paper so we have to consider at the time of birth of the baby number of boys = 5
And then their average age was 60/5 = 12 years.
If both 10 & 12 are available in option, then 10 will gate more priority.