1.

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 A. 20 years B. 28 years C. 15 years D. 21 years

Answer»

Let the ages of A and B be 5x and 7x

\(\Rightarrow \frac{5\text{x + 4}}{7\text{x} \,+ \,4}=\frac{3}{4}\)

By cross multiplication 

⇒ 4(5x + 4) = 3(7x + 4) 

⇒ 21x - 20x = 16 - 12 

⇒ x = 4 

Age of B = 7x = 28 years



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