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Predictions and Probability

If there are 15 blue marbles, 5 red marbles, and 10 green marbles in a bag, what color marble do you think you will pull out of the bag? What is the probability of this occurring? What is the probability of pulling out a green marble?

When working probability problems it is easier to catch mistakes by making initial predictions before calculating probability.

There are more blue marbles than any other color we can predict that we would pull out a blue marble. Probability is the ratio of successful outcomes to total outcomes. This can be expressed as a fraction:

$\frac{number\ of\ possible\ successful\ outcomes}{number\ of\ total\ outcomes}$

Probability of getting a blue marble is:

$\frac{total\ number\ of\ blue\ marbles}{total\ number\ of\ marbles}$

$\frac{15}{30}=\frac{1}{2}$

Probability of getting a blue marble is 50%.

Probability of getting a green marble is: $\frac{10\ green\ marbles}{30\ marbles}=\frac{1}{3}=33.3\%$