PSAT Math Grid-Ins Question 55: Answer and Explanation

Question: 55

Daniel works for a pest control company and is spraying all the lawns in a neighborhood. The figure above shows the layout of the neighborhood and the times that Daniel started spraying the lawns at two of the houses. Each lawn in the neighborhood is approximately 0.2 acres in size and takes the same amount of time to spray.

How many minutes will it take Daniel to spray all of the lawns in the neighborhood?

Correct Answer: 252

Explanation:

252

Difficulty: Medium

Category: Problem Solving and Data Analysis/Rates, Ratios, Proportions, and Percentages

Getting to the Answer: Break the question into steps. First, find how long it took Daniel to spray one lawn, and then use that amount to find how long it took him to spray all the lawns. According to the figure, he started the first house at 9:00 and the sixth house at 10:00, so it took him 1 hour, or 60 minutes, to spray 5 houses. This gives a unit rate of 60 ÷ 5 = 12 minutes per house. Count the houses in the figure—there are 21. Multiply the unit rate by the number of houses to get 12 × 21 = 252 minutes to spray all the lawns.