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.)

The correct answer is . 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 + 37, or 50. Since there are 13 red pens in the box, it follows that the probability of selecting a red pen is . Note that 13/50 and .26 are examples of ways to enter a correct answer.