First, write the equation system based on the problem
For an instance, r stands for Raju's present age and f stands for father's present age
"Raju's father is 4 times as old as Raju" could be written as
⇒ f = 4r (first equation)
"After 5 years, father will be three times as old Raju" could be written as
⇒ f + 5 = 3(r + 5) (second equation)
Second, solve the problem using substitution method
Substitute f on the second equation with 4r from the first equation in order to find the value of r
f + 5 = 3(r + 5)
4r + 5 = 3(r + 5)
4r + 5 = 3r + 15
4r - 3r = 15 - 5
r = 10
Substitute the value of r to the first equation in order to find the value of f
f = 4r
f = 4(10)
f = 40
In the present, Raju is 10 years old and Raju's father is 40 years old
