Madhya Pradesh Police Exam Model Paper 5

Given:
Average age of A, B, C, D = 8 years
Average age of A, B, D, E = 7 years
Age of C = 9 years
Formula used:
Sum of ages = (Average) × (Total number of person)
Calculation:
Sum of ages of A, B, C, D = (Average of A, B, C, D) × 4
⇒A+B+C+D=8×4=32 years
⇒A+B+9+D=32
⇒A+B+D=23 ….(1)
Sum of ages of A, B, D, E = (Average of A, B, D, E) × 4
⇒A+B+D+E=7×4=28
⇒23+E=28 [using eqn. 1]
⇒ E = 5 years
∴ The age of sister is 5 years.