The average age of Ravi and his two children is 23 years and the average age of Ravi's wife and the same children is 21 years. If the age of Ravi is 42 years, the age of his wife is :

39 years 

Age of Ravi = 42 years

The average age of Ravi and his two children = 23 years

⇒ Total ages of (Ravi + two children ) = 23 × 3 =   69 years .... ( 1 )

And the average age of Ravi’s wife and the same children = 21 years.

⇒ Total age of ( His wife + two children) =  21 × 3 = 63 years .... ( 2 )

From equation  ( 1 ) - ( 2 ) , we get

∴ Ravi – Ravi's wife = 3 years

⇒ 42 – wife = 3 years

∴ Wife = 42 – 3 = 39 years