The ages of Hari and Harry are in ratio 5:7. Four years from now the ratio of their ages will be 3:4. Find their present ages.

Let ratio (common) be x
∴Hari's age: 5x, Harry's age → 7x
and four years later: Ages will be 5x+4 and 7x+4
As per the question:
5x+4/7x+4 = 3/4
4(5x+4) = 3(7x+4)
20x+16 = 21x+12
20x - 21x = 12 - 16
-1x = -4
x = 4
Hari's age = 5x = 5 × 4 = 20 years
Harry's age = 7x = 7 × 4 = 28 years