Chapter 4 - Proportions, Percents, and Solving Inequalities - 4.3 - More on Percents and Problem Solving - Problem Set 4.3 - Page 162: 48

The rate of profit based on the cost is 30%.

Let r represent the rate of profit. We can use the following guideline to solve this problem: Selling price = Cost + Profit So: 31.20 = 24 + r $\times$ 24 31.20 = 24 + 24r 7.2 = 24r Divide both sides by 24: r = 0.3 Multiply this amount by 100% to convert it into percent. So, 0.3 $\times$ 100% = 30% The rate of profit based on the cost is 30%.