Percent of Change Tuesday, October 19, 2010

Lesson Objectives  Find percent of change (percent of increase or percent of decrease)

Real-Life Connection  What things in everyday life are described as % increases or % decreases?

What things in everyday life are described as percent increases or decreases?  Fuel prices (example: The cost of gas might increase by 10% over a major holiday weekend)  Other product prices (example: You might go shopping and find a sweater that’s 20% off)  The stock market (example: You may read in the newspaper that a corporation’s shares have risen 1.8%)

Any increase or decrease can be represented as a percent!

Vocabulary  A percent of change is a ratio  It compares the change in quantity to the original amount

change in quantity __________________ original amount change in quantity __________________ original amount

This is your formula for finding percent of change! change in quantity _______________ original amount change in quantity _______________ original amount

Vocabulary  If the original amount goes up, or increases, then it is a percent of increase  If the original amount goes down, or decreases, then it is a percent of decrease

Example 1  Let’s say you are shopping for a jacket  The original cost of the jacket is $50  The jacket is on sale for $35  Is this situation an increase or decrease?

Example 1  Use the percent of change formula to find the percent of decrease in the cost

Example 1 – step one: apply the formula change in cost = $50 – 35 = $ 15 ___________ _______ ____ original cost $50 $50

Example 1 – step two: convert the ratio to a percent $ ___ or ___ = ___ = 30% $

Example 1 – solution The price of the jacket was decreased by 30% In other words, the jacket was on sale for 30% off

Example 2 Rita weighed 120 pounds on Thanksgiving. On New Year’s Day, she weighed 130 pounds. Find the percent of change in Rita’s weight from Thanksgiving to New Year’s Day and state whether it is an increase or a decrease.

Example 2 – step one: apply the formula change in weight = 130 – 120 = 10 _____________ _______ ____ original weight

Example 2 – step one: convert the ratio to a percent ___ = % or 8.3% 120

Example 2 – solution From Thanksgiving to New Year’s Day, Rita’s weight increased by approximately 8.3% From Thanksgiving to New Year’s Day, Rita’s weight increased by approximately 8.3%

Let’s Review! 1. What is the formula for finding percent of change?

Let’s Review! 1. What is the formula for finding percent of change? change in quantity _______________ original amount

Let’s Review! 2. What do you do with the ratio you get after you have applied the formula?

Let’s Review! 2. What do you do with the ratio you get after you have applied the formula? Convert it to a percent!

Let’s Review! 3. How do you know if it’s a percent of increase or a percent of decrease?

Let’s Review! 3. How do you know if it’s a percent of increase or a percent of decrease? Did the original amount go up or down?