## DaniRae231 2 years ago You flip three coins. What is the probability that you get at least two tails, given that you get at least one tail?

It's heads or tails, so it's a binomial distribution. So we use the formula: ${n \choose r}{p^r}{(1-p)^{n-r}}$ where n is the number of trials (3) and r is the number of successes (tails). ${3 \choose 2}{0.5^2}{(1-0.5)^{3-2}}={3 \choose 2}{(0.25)}{(0.5)}={3 \choose 2}(0.125)$ ${n \choose r}={n! \over {r!(n-r)!}}={3! \over 2!1!}={{1*2*3} \over 1*2*1}=3$ So, $3*0.125=0.375=P(X=2)$