# 8.4 Percent of Increase and Decrease. Percent change is the ratio of the amount of change to the original amount. Percent increase describes how much.

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8.4 Percent of Increase and Decrease

Percent change is the ratio of the amount of change to the original amount. Percent increase describes how much the original amount increases. Percent decrease describes how much the original amount decreases. amount of change original amount percent change =

Find the percent increase or decrease from 16 to 12. Is this percent an increase or decrease? 16 – 12 = 4First find the amount of change. Think: What percent is 4 of 16? amount of decrease original amount 4 16 Set up the ratio.

Continued = 25% Write as a percent. Reduce the fraction or find the decimal form. 4 16 From 16 to 12 is a 25% decrease. = 1 4

Find the percent of increase or decrease from 15 to 20. Try This: Is this percent an increase or decrease? 20 – 15 = 5First find the amount of change. Think: What percent is 5 of 15? amount of increase original amount 5 15 Set up the ratio.

Continued = 33 1 %Write as a percent. = 0.33…Find the decimal form. 5 15 From 15 to 20 is a 33 % increase. Reduce the fraction if possible. 1 3 3 3 1

Sarah bought a DVD player originally priced at \$450 that was on sale for 20% off. What was the sale price? Percent Decrease \$450  20%First find 20% of \$450. \$450  0.20 = \$9020% = 0.20 The amount of decrease is \$90. Think: The reduced price is \$90 less than \$450. \$450 – \$90 = \$360Subtract the amount of decrease. The sale price of the DVD player was \$360.

Mr. Olsen has a computer business in which he sells everything at 40% above the wholesale price. If he purchased a printer for \$85 wholesale, what will be the retail price? Percent Increase \$85  40% First find 40% of \$85. \$85  0.40 = \$3440% = 0.40 The amount of increase is \$34. Think: The retail price is \$34 more than \$85. \$85 + \$34 = \$119 Add the amount of increase. The retail price of this printer will be \$119.

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