#### Answer

$\frac{1}{4}$

#### Work Step by Step

P(E) = $\frac{no.\ of\ outcomes\ in\ favor}{Total\ no.\ of\ outcomes}$
Given that H is heads and T is tails, the set of equally likely outcomes is:
S = {HH, HT, TH, TT}.
E: two tails
Favorable outcomes= {TT}
P(E) = $\frac{1}{4}$