Mathematics 9709 · AS & A Level · Linear combinations of random variables

Linear combinations of random variables — practice question

A spinner has $5$ equal sectors, labelled $1$, $2$, $3$, $4$ and $5$. The number on the sector where it stops is taken as the score. This score is represented by the random variable $X$, and its probability distribution is listed in the table: $P(X=1)=0.3$, $P(X=2)=0.15$, $P(X=3)=3p$, $P(X=4)=2p$, $P(X=5)=0.05$. There is also a second spinner with $3$ sectors, labelled $1$, $2$ and $3$. The score from this spinner is represented by the random variable $Y$. It is known that $P(Y=1)=0.3$, $P(Y=2)=0.5$ and $P(Y=3)=0.2$.
(i)[1]

Find the value of $p$.

(ii(a))[3]

Find the probability that, when both spinners are spun together, the sum of the scores is $4$.

(ii(b))[3]

Find the probability that, when both spinners are spun together, the product of the scores is less than $8$.

Worked solution & mark scheme

This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: The correct value is $p=0.1$

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