Ans -

There are total n nodes . Here out of the n nodes except the leaves and root all the others have both the child and parent . Let us assume that the heigh of the binary tree is h.

Then h log n ( Base 2) .[ floor value ] .

No of leaves 2^log n (base 2 ).

Hence the no of nodes having both the parent and child is

n-2^log n (base 2 ) -1