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2.3.10 Conditional probabilities (A-level only)

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Question 21

Two boxes, X X\,X and YYY, contain red, blue, and green pens. Box X X\,X contains 2 red pens, 5 blue pens, and 3 green pens. Box Y Y\,Y contains 6 red pens, 2 blue pens, and 2 green pens. Casey picks one pen at random from Box X X\,X and places it into Box YYY. Casey then picks one pen at random from Box YYY.

a.

Draw a tree diagram to represent this information.

[2]
b.

Find the probability that Casey picks two pens of the same colour.

[2]
c.

Given that both pens are the same colour, find the probability they are both blue.

[2]

2.3.10 Conditional probabilities (A-level only) Questions

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