An ordinary fair die is thrown until a 6 is obtained. Two ordinary fair dice are thrown together until a pair of $$\(6 \mathrm{~s}\)$$ is obtained. The number of throws taken is denoted by the random variable $$\(X\)$$. Find the expected value of $$\(X\)$$. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................

Mathematics
IGCSE&ALevel
CAIE
Exam No:9709_w20_qp_53 Year:2020 Question No:2(b)

Answer:

36

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.)

Solution:

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