Question

A basket contains 12 black marbles and 8 blue marbles. What is the probability Josiah will

select a blue marble, replace it, and then a black marble? Express your answer as a percent.

Answer 1

• 24%

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Given

• Black marbles = 12,
• Blue marbles = 8.

Solution

Total number of marbles:

• 12 + 8 = 20

Probability of selecting a blue marble:

• P(blue) = number of blue / total = 8/20 = 2/5

Probability of selecting a black marble after replacing the blue:

• P(black) = number of black / total = 12/20 = 3/5

Probability of selecting blue and black marbles in same order with replacement:

• P(blue, then black) = 2/5*3/5 = 6/25 = 24/100 = 24%