total no. of children = 40

∴ the median is the mean of marks of 20^th and 21^st child.

both lies in the range of 20-30.

let’s assume a uniform distribution of marks.

i.e., 14^th child has 20 marks and 15^th child has 20 + marks.

⇒ marks of 15^th child =

⇒ marks of 20^th child =

⇒ marks of 20^th child = 25

also, marks of 21^st child =

median =

median =