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

Linear combinations of random variables — practice question

Tim rolls a fair die two times and records the number on each roll.
(i(a))[1]

Tim works out his final score in the following way. If the number on the second throw is a $5$ he multiplies the two numbers together, and if the number on the second throw is not a $5$ he adds the two numbers together. Find the probability that his final score is $12$.

(i(b))[3]

Tim works out his final score in the following way. If the number on the second throw is a $5$ he multiplies the two numbers together, and if the number on the second throw is not a $5$ he adds the two numbers together. Find the probability that his final score is $5$.

(ii)[5]

Events $A$, $B$, $C$ are defined as follows: $A$: the number on the second throw is $5$; $B$: the sum of the numbers is $6$; $C$: the product of the numbers is even. Use calculation to decide which pairs, if any, of the events $A$, $B$ and $C$ are independent.

Worked solution & mark scheme

This 9-mark question has a full step-by-step worked solution and mark scheme. One marking point: Correct probability is $P(6,6)=\frac{1}{36}$

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