binary tree problem

Question

11. A binary tree has n leaf nodes. The no. of nodes of degree 2 in this tree is:

(a) log₂n (b) n-1 (c) n (d) 2n

Answer 1

take example of 7 nodes 
level 0 : 2⁰=1 node
level 1 : 2¹=2 nodes
level 2 : 2²=4 nodes 
total =1+2+4=7 nodes 
here leaf n=4 , no of nodes with degree 2 =3
option (a) log₂n=log₂(4)=2 FALSE
option (b) n-1=4-1=3 TRUE
option (c) n=4 FALSE
option (d) 2n=2*4=8 FALSE
hence Ans is B

Comments

degree of a node = no of children it have