PSAT Math Multiple-Choice Question 358: Answer and Explanation

Question: 358

Kelania owns a bakery, and she adjusts the number of pounds of flour she orders each week based on the number she used the previous week. After the first week of the month, she decreased the number of pounds of flour she ordered by 25 percent, then increased the number by 10 percent the following week, then increased the number by an additional 50 percent in the last week of the month. What is the approximate total percent increase in the number of pounds of flour Kelania ordered from the start of the month until the end of the month?

• A. 20%
• B. 24%
• C. 30%
• D. 35%

Correct Answer: B

Explanation:

B

Difficulty: Medium

Category: Percent Change

Getting to the Answer: Remember to avoid merely adding the percentages together. Find each change individually. You're not given a definite number of pounds of flour in the question, so assume Kelania starts with 100. To save a step with each change, calculate the total amount instead of the weekly increase or decrease. The first change is -25%; so the number of pounds of flour ordered the next week is 75% × 100 = 0.75 × 100 = 75. The second change is +10%, which corresponds to 110% × 75 = 1.1 × 75 = 82.5 pounds. The final change is +50%, which means there are now 150% × 82.5 = 1.5 × 82.5 = 123.75 pounds. The percent change is . Now, round to the nearest percent and you get 24%, which is (B).