(a)[2]
Find the probability that two tails occur for the first time on the 7th throw.
(b)[2]
Find the probability that it takes more than 9 throws to obtain two tails for the first time.
Mathematics 9709 · AS & A Level · Discrete random variables
Discrete random variables — practice question
Two fair coins are tossed together. The random variable $X$ represents the number of paired tosses needed until two tails are seen at the same time for the first time.
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This 4-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Applies the correct binomial probability method, for example $(1-p)^6p$ with $0 \le p \le 1$.” …
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