You toss two coins. What is the probability P that both are tails?

Answer 1

1/4

Answer 2

prob that first is tails = 0.5
The second toss is independent of the first so also 0.5 so 0.5*0.5
= 0.25 = 1/4

Which you did not need algebra for.
You have 4 equally likely outcomes
HH
TT
HT
TH

so p(TT) = 1/4