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    IBMediumProbability7–9

    Two Counters of the Same Colour

    Duas Fichas da Mesma Cor

    A bag holds 55 red counters and 33 blue counters. Two counters are drawn one after the other, without replacement. Find the probability that the two counters are the same colour.

    Two different routes give the same colour, so the event splits into cases you add. Within each case the second draw happens in a bag that has already changed.

    Solution

    Step 1 of 7

    1. 1.Both red: