Mathematics 9709 · AS & A Level · Discrete random variables
Discrete random variables — practice question
Each day, Richard boards a flight from Astan to Bejin. For any one day, the chance that the flight is early is $0.15$, the chance that it is on time is $0.55$ and the chance that it is late is $0.3$.
(a)[1]
Find the probability that, on each of $3$ days chosen at random, Richard’s flight does not arrive late.
(b)[3]
Find the probability that, for $9$ days chosen at random, Richard’s flight arrives early at least $3$ times.
(c)[5]
A random sample of $60$ days is taken. Use an approximation to determine the probability that Richard’s flight arrives early at least $12$ times.
Worked solution & mark scheme
This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Accurate calculation of $(0.7)^3=0.343$ (or an equivalent binomial method).” …