PSAT Math Multiple-Choice Question 117: Answer and Explanation

Question: 117

Every fifteen minutes, a lab assistant can centrifuge 3 vials of blood. If she continues at this rate, how many vials of blood will she centrifuge in 4 hours?

• A. 12
• B. 20
• C. 32
• D. 48

Correct Answer: D

Explanation:

D

The question asks for the number of vials a lab assistant can centrifuge in a certain amount of time. Begin by reading the question to find information on the centrifuge rate. The question states that every fifteen minutes, a lab assistant can centrifuge 3 vials of blood. First, convert hours to minutes. Each hour has 60 minutes, so there are 4(6) = 240 minutes in 4 hours. Set up a proportion to determine the number of vials she can centrifuge in 4 hours, making sure to match up the units: . Cross-multiply to solve for x: 15x = 720. Divide both sides of the equation by 15 to get x = 48 vials. The correct answer is (D).