Delhi Police Constable Exam Model Paper 2

Given,5 years ago average age of five persons = 20 years
Formula:
Average = Sum of all observations/total number of all observations
Calculation:
Sum of age of five persons 5 years ago $=20\times 5=100$ years
Sum of present age of five persons = $100+5\times 5=125$ years
If a person of age 31 years joined the group, then sum of age of six persons = $125+31=156$
∴ Average age of six persons = $\frac{156}{6}=26$ years