Fifteen years from now Ravi's age will be four times his present age. What is Ravi's present age?

Let Ravi's present age be x.
Fifteen years later, Ravi's age = 4 × x
x + 15 = 4x
15 = 4x - x
15 = 3x
∴ x = 5
Ravi's present age is 5 years.