Question

The ages of A and B are in the ratio 5:7. Four years from now the ratio of their ages will be 3:4. The present age of B is

Answer 1

Answer:

28 years

Step-by-step explanation:

let their ages be 5x and 7x

$\frac{5x + 4}{7x + 4} = \frac{3}{4} \\ \\ 20x + 16 = 21x + 12 \\ 4 = x \\ \\ present \: age \: of \: b = 4 \times 7 = 28$

Answer 2

Answer:

Let the present ages of A and B be 5x and 7x respectively.

After four years the ratio of their ages is 3:4

⇒5x + 4 7x+4=3 4

By cross multiplication 

⇒ 4(5x + 4) = 3(7x + 4) 

⇒ 21x - 20x = 16 - 12 

⇒ x = 4 

Age of B = 7x = 28 years