Madhya Pradesh Police Exam Model Paper 7

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 $=12\times 4=48$
Since the average increases by 5 so new average becomes 17
So total age of all 5 including teacher $=17\times 5=85$
The age of teacher $=85-48=37$ yrs
∴ The age of the teacher is 37 yrs.