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Question Video: Determining the Theoretical Probability of an Event in a Marbles Problem Mathematics

A bag contains 7 white marbles, 8 black marbles, and 7 red marbles. If a marble is chosen at random from the bag, what is the probability that it is white?

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Video Transcript

A bag contains seven white marbles, eight black marbles, and seven red marbles. If a marble is chosen at random from the bag, what is the probability that it is white?

We can recall that to find the probability of an event occurring, we take the number of favorable outcomes and divide it by the total number of outcomes. Here, we’re asked to calculate the probability of getting a white marble. And we can write this as 𝑃 brackets 𝑊 for white. We then need to establish how many white marbles there are. And we’re told that there are seven. So this will be the value on the numerator. The value on the denominator will be the total number of marbles. So we’re told that there are seven white, eight black, and seven red. So we add these values together. This gives us the fraction seven over 22. We can’t simplify this fraction any further. So the probability of getting a white marble is seven over 22.

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