Question

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

Answer 1

1/4

Answer 2

For any two events A and B, with P(B) ≠ 0, then the conditional probability of A given B is:

P(A | B) = P( A ∩ B) / P(B)

Let A be the event of two tails
Let B be the event at least one tail

Possible outcomes are:
HH, HT, TH, TT

P(A ∩ B ) = P( HH ) = 1/4
P(B) = P( HT, TH, TT) = 3/4

P( A | B ) = (1/4) / (3/4) = 1/3

Answer 3

got it wrong..The coins can land four ways, HH, HT, TH, or TT.

TT is 1 way OUT OF 4 ways, so the probability is
1 way OVER 4 ways or .

Answer 4

If both are fair coins the probability of tails is 0.5 for each coin. The outcomes are independent, therefore the probability of both tails is:
\[P(both\ tails)=\frac{1}{2}\times \frac{1}{2}=?\]

Answer 5

common sense : you have 4 possibilities HH, HT, TH, TT out of which TT's probability is 1/4