Mathematics 9709 · AS & A Level · Discrete random variables
Discrete random variables — practice question
Eighty percent of the people living in Kinwawa support the idea of a leisure centre being constructed in the town. Twenty Kinwawa residents are picked at random and, one by one, are asked whether they are in favour of the leisure centre.
(a)[3]
Calculate the probability that more than $17$ of these residents support the leisure centre.
(b)[1]
Find the probability that the $5$th person asked is the first person who is not in favour of the leisure centre.
(c)[2]
Find the probability that the $7$th person asked is the second person who is not in favour of the leisure centre.
Worked solution & mark scheme
This 6-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Apply the correct binomial method for $P(X>17)$, for example $\sum_{x=18}^{20} \binom{20}{x}(0.8)^x(0.2)^{20-x}$ or the complementary method” …