When you flip a coin twice, you have a 50/50 chance of it land on heads or tails.
The possible combinations for fliping a coin twice:
HH (heads/heads both times)
T/H(Tails/Heads)
H/T(Heads/Tails)
or the one you're looking for...
T/T (Tails/Tails both times)
You have a 1/4 chance of getting tails both times.
