A pair of fair coins is thrown repeatedly until a pair of tails is obtained. The random variable $$$X$$$ denotes the number of throws required to obtain a pair of tails. Find the expected value of $$$X$$$. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................

Mathematics

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CAIE

Exam No：9709_s20_qp_53 Year：2020 Question No：5(a)

Answer:

$\frac{1}{\frac{1}{4}}=4$

Knowledge points:

5.4.3 use formulae for the expectation and variance of the binomial distribution and for the expectation of the geometric distribution. (Proofs of formulae are not required.)

Answer:

Knowledge points:

Solution:

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