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Problem-Solving and Data Analysis / Probability and conditional probability Difficulty: Medium

A box contains $13$ red pens and $37$ blue pens. If one of these pens is selected at random, what is the probability of selecting a red pen? (Express your answer as a decimal or fraction, not as a percent.)

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Explanation

The correct answer is $StartFraction 13 Over 50 EndFraction$ . It's given that a box contains $13$ red pens and $37$ blue pens. If one of these pens is selected at random, the probability of selecting a red pen is the number of red pens in the box divided by the number of red and blue pens in the box. The number of red and blue pens in the box is $13 plus 37$ , or $50$ . Since there are $13$ red pens in the box, it follows that the probability of selecting a red pen is $StartFraction 13 Over 50 EndFraction$ . Note that 13/50 and .26 are examples of ways to enter a correct answer.