Mathematics 9709 · AS & A Level · Probability

Probability — practice question

A standard fair $6$-sided die is used in a game. The player rolls once. If the outcome is $2$, $3$, $4$ or $5$, that number becomes the score and there is no second roll. If the outcome is $1$ or $6$, the player rolls again and the score is the total of the two results from the two rolls. Events $A$ and $B$ are defined as follows. $A$: the player's score is $5$, $6$, $7$, $8$ or $9$. $B$: the player has two throws.
(a)[2]

Draw a tree diagram with full labels to show this information.

(b)[3]

Show that $P(A)=\frac{1}{3}$.

(c)[2]

Determine whether events $A$ and $B$ are independent or not.

(d)[3]

Find $P(B\mid A')$.

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: The first throw on the tree diagram is completely correct, with six branches each having probability $\frac{1}{6}$.

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