ncert q no. 4 ex 13.4 here x(tt)=0 then p(tt)=1/4 how plz explain sir....

X(TT) = 0

Here, 

Let X represents the number of heads.

So, P(X=0) = P(TT) = 1/4

 

[Since, it is the probability of selecting 0 heads, i.e, 2 tails.

Sample space = {HH, HT, TH, TT}

So, P(TT) = 1/4]