(a)[2]
Find the probability that the two marbles chosen are the same colour.
(b)[3]
Find the probability that the first marble is blue, given that the second marble is red.
Mathematics 9709 · AS & A Level · Probability
Probability — practice question
A bag has $4$ blue marbles and $12$ red marbles. A marble is chosen at random from the bag. If the marble picked is blue, it goes back into the bag, but if it is red, it is left out. A second marble is then chosen at random from the bag.
Worked solution & mark scheme
This 5-mark question has a full step-by-step worked solution and mark scheme. One marking point: “A correct probability expression for drawing two balls of the same colour, e.g. $\frac{4}{16}\times\frac{4}{16}+\frac{12}{16}\times\frac{11}{15}$.” …
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