(a) A fair coin is tossed until the first H occurs. Compute the probability that three tosses are required.
(b) A fair coin is tossed until the second H occurs. Compute the probability that five tosses are required.
(c) A coin with $P(\text{heads})=\frac{2}{3}$ is tossed until the third T. Find the probability of five heads.
for (a) there is only possible case : TTH , Since $3$ Tosses are required, The probability is $1\times (0.5)\times (0.5)\times (0.5)$
for (b) there are $4$ possibilities then the probability will be $4\times (0.5)^5$
for (c) I have no clue what to do with the third case.