The average age of a man and his two twin sons born on the same day is 30 yr. The ratio of the ages of father and one son is 5 : 2, What is the father's age?

According to the question,
Average age of man and his twin sons = 30
∴ Total age = 30 x 3 = 90 yr.
According to the question,
Ratio of father and one son = 5 : 2
∴ Ratio of father and both the sons = 5 : 2 : 2
(As sons are born on the same day.)
∴ 5k + 2k + 2k = 90 or 9k = 90
∴ k = 10
∴ Age of father = 5 x 10 = 50 yr.