Question

Four years ago the average age of A,B and C was 25 years. Five years ago the average age of B and C was 20 years. A's present age is ​

Answer 1

Given :

• Four years ago the average age of A,B and C was 25 years. Five years ago the average age of B and C was 20 years.

To find :

• A's present age is 

Solution :

Present average of A, B, C

= 25 + 4

= 29 years

Present average age of B and C

= 20 + 5

= 25 years

A's present age

= 3 × 29 - 2 × 25

= 87 - 50

= 37 years

Alternative method:

A's present age

= 29 + 2 × (29 - 25)

= 29 + 2 × 4

= 29 + 8

= 37 Years

Answer 2

Question:

Four years ago the average age of A,B and C was 25 years. Five years ago the average age of B and C was 20 years. A's present age is 

Solution:

Four years ago, average age of A,B,C = 25

Five years ago, average age of B and C = 20

ATP

(A+B+C)/3 = 25

=) A+B+C = 25×3 = 75

(B+C)/2 = 20

=) B+C = 20×2 = 40

Four years ago, total age of A,B,C = 75

Five years ago, age of B,C = 40

We will subtract (1+1+1) from the total age to get their five years ago's age

Five years ago, their total age = (75-3) = 72 yrs

To find A's age five years ago

ATP

A+B+C = 72

=) A+40 = 72

=) A = 72-40 = 32

Five years ago, A's age = 32 yrs

To get the present age of A, we have to add 5 with 32(i.e A's five years ago's age)

Therefore, present age of A = (32+5)yrs = 37yrs