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First Year maths · Y.5 · Compound events

Probability of two independent events with replacement

The first draw is put back, so the two draws do not affect each other. Multiply the two probabilities.

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  1. A bag has 11 red and 1 blue marbles. A marble is drawn, put back, and a second marble is drawn. What is the probability that both are red? Write a fraction in lowest terms.

    Answer: 121/144

  2. A bag has 11 red and 5 blue marbles. A marble is drawn, put back, and a second marble is drawn. What is the probability that both are red? Write a fraction in lowest terms.

    Answer: 121/256

  3. A bag has 3 red and 6 blue marbles. A marble is drawn, put back, and a second marble is drawn. What is the probability that both are red? Write a fraction in lowest terms.

    Answer: 1/9

Tip: The first draw is put back, so the two draws do not affect each other. Multiply the two probabilities.

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