A father is 5 times as old as his son. His son is 6 years old. After how many years, will the father be 4 times as old as his son?

Age of son = 6 years
Age of father = 6 × 5 = 30 years
Let after P years father will be 4 times of son.
According to question ,
⇒ 30 + P = 4 (6 + P)
⇒ 4P – P = 30 – 24
⇒ 3P = 6
⇒ P = 2 years
Hence, after 2 years father will be 4 times of son.