Mathematics 9709 · AS & A Level · Discrete random variables
Discrete random variables — practice question
Every day, Salah chooses to try the crossword puzzle in his newspaper. On any one day, the chance that he completes the puzzle is $0.65$, and the days are independent of each other.
(a)[1]
Find the probability that Salah completes the puzzle for the first time on the $5$th day.
(b)[2]
Find the probability that Salah completes the puzzle for the second time on the $5$th day.
(c)[3]
Find the probability that Salah completes the puzzle fewer than $5$ times in a week ($7$ days).
(d)[5]
Use a suitable approximation to find the probability that Salah completes the puzzle more than $50$ times in a period of $84$ days.
Worked solution & mark scheme
This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Correct probability value $(0.35)^4\times0.65=0.00975$” …