Question

The ratio between as and bs ages two years ago was 3:2 and at present its 7:5.Find b's present age?

Answer 1

let present ages be 7x and 5x. Go back 2 years . 7x-2 and 5x-2. now
$(7x - 2) \div (5x - 2) = 3 \div 2 \\ now \: cross \: multiply \\ (7x - 2) \times 2 = (5x - 2) \times 3 \\ 14x - 4 = 15x - 6 \\ x = 2$
The age of b is 5*2 i.e. 10 years.