PSAT Math Multiple-Choice Question 242: Answer and Explanation

Question: 242

The white-footed mouse, named for its darker body fur and white feet, is primarily found on the east coast of the United States, living in warm, dry forests and brushland. A scientist in Virginia studied a sample of 200 white-footed mice to see how many offspring they had per birth. The results of the study are recorded in the figure above. Based on the data, given a population of 35,000 female white-footed mice living in Virginia, how many would you expect to have a litter of seven or more pups?

• A. 3,325
• B. 4,375
• C. 7,700
• D. 15,400

Correct Answer: C

Explanation:

C

Difficulty: Medium

Category: Problem Solving and Data Analysis/Statistics and Probability

Getting to the Answer: Read the question, identifying parts of the graphic you need—the question asks about litters of 7 or more pups, so you'll only use the heights of the bars for 7, 8, and 9 pups. Start by finding the percent of the mice in the study that had a litter of 7 or more pups. Of the 200 mice in the sample, 25 + 14 + 5 = 44 had a litter of 7 or more pups. This is of the mice in the study. Given the same general conditions (such as living in the same geographic region), you would expect approximately the same results, so multiply the number of female mice in the whole population by the percent you found: 35,000 × 0.22 = 7,700. Choice (C) is correct.