Question

the age of A and B are in the ratio 5:7 four years from now the ratio of their ages will be 3:4 then the present age of B is?

Answer 1

let the age of A and B are 5x and 7x
according to question
5x+4/7x+4 = 3/4. ( cross multiplication )
4(5x+4) = 3(7x+4).
20x + 16 = 21x + 12
20x - 21x = 12 - 16
-x = -4. ( minus to minus cancel )
x = 4
ages are
5×4 = 20
7×4 = 28
age of A = 20
age of B = 28

Answer 2

Answer:

28 years

Step-by-step explanation:

Let present ages of A and B be 5x and 7x, respectively [ Ratio is 5:7]

After four years their ages will be (5x + 4) and (7x + 4)

According to question

(5x + 4) : (7x + 4) = 3 : 4

$\frac{5x+4}{7x+4}=\frac{3}{4}$

4(5x + 4) = 3(7x + 4)

20x + 16 = 21x + 12

21x - 20x = 16 - 12

x = 4

∴ Present age of B (7x) = 28 years