Chapter 4 - Proportions, Percents, and Solving Inequalities - 4.2 - Percents and Problem Solving - Problem Set 4.2 - Page 156: 48

If he decides to buy the new car, the percent change in his monthly car payment will be 15%. It is a percent increase.

To find the percent change, we use the following formula: percent change = $\frac{New\ amount\ -\ Original\ amount}{Original\ amount}$ $\times$ 100% The original monthly car payment is 300 dollars. The new monthly car payment will become 345 dollars. Substituting these values into the formula yields: percent change = $\frac{345\ -\ 300}{300}$ $\times$ 100% percent change = $\frac{45}{300}$ $\times$ 100% percent change = 0.15 $\times$ 100% percent change = 15% Because the percent change is a positive number, it is a percent increase.