PSAT Math Multiple-Choice Question 546: Answer and Explanation

Question: 546

Which of the following mammals covers a distance closest to the combined distance covered by a cheetah running for 15 min and a giraffe running for 5 min?

• A. Zebra running for 30 minutes
• B. African wild dog running for 20 minutes
• C. Lion running for 50 minutes
• D. Elephant running for 60 minutes

Correct Answer: A

Explanation:

A

The question asks for the animal running for a specified period of time that covers a distance that is equivalent to the sum of two other animals' distances over specified periods of time. Use Bite-Sized Pieces and Process of Elimination to tackle this question. Begin by calculating the distance covered by a cheetah running for 15 min and a giraffe running for 5 min. Set up a proportion to determine the distance covered by a cheetah in 15 minutes, being sure to match up units: . Cross-multiply to get 10x = 270, then divide both sides by 10 to get x = 27 km. Repeat the process to determine the distance covered by a giraffe in 5 minutes: , which becomes 10x = 45, or x = 4.5 km. The total distance covered by a cheetah and a giraffe in the specified time periods is 27 km + 4.5 km = 31.5 km. Use a proportion to calculate the distance covered by each animal in each answer choice, and eliminate answer choices that are not close to this value. Choice (A) becomes , then 10x = 330, or x = 33 km. Keep (A) for now, as it is very close to the target value of 31.5, but check the remaining answer choices to see if one is closer. Choice (B) becomes , then 10x = 240, or x = 24 km. Eliminate (B), as it is not closer to 31.5 km than (A). Choice (C) becomes , then 10x = 700 km, or x = 70 km. Eliminate (C). Choice (D) becomes , then 10x = 420 km, or x = 42 km. Eliminate (D). The correct answer is (A).