Correct Answer - Option 2 : 37
Given:
The average age of four sisters is 12 yr. If the age of their teacher be also included, the average is increased by 5 year.
Formula:
Average of n numbers a1, a2, .. …. an = (a1 + a2 + ... + an)/n
Calculation:
Total age of 4 sisters = 12 × 4 = 48
Since the average increases by 5 so new average becomes 17
So total age of all 5 including teacher = 17 × 5 = 85
The age of teacher = 85 - 48 = 37 yrs
∴ The age of the teacher is 37 yrs.