Percent Change

Percent of Change Formula Percent of ChangeNew # – Original # Original #100 =

A CD at a local store had its price changed from $10 to $8. What was the percent of change of the price of the CD? Original Number: New Number: Substitute these into the formula for percent of change: 10 8 Percent of Change10 – =

A CD at a local store had its price changed from $10 to $8. What was the percent of change of the price of the CD? (8 - 10) x 100 ÷ 10 = -20 There was a 20% decrease in the price of the CD. Percent of Change =

After stopping at a bus stop, the number of students sitting on the bus changed from16 to 20. What is the percent of change in the number of students on the bus? Original Number: New Number: Substitute these into the formula for percent of change: Percent of Change20 – =

What is the percent of change in the number of students on the bus? ( ) x 100 ÷ 16 = 25 There was a 25% increase in the number of students on the bus. Percent of Change20 – = After stopping at a bus stop, the number of students sitting on the bus changed from16 to 20.

The percent of change from 12 to 16 is different than the percent of change from16 to  16 Original Number : 12 New Number : 16 33% Increase 16  12 Original Number : 16 New Number : 12 25% Decrease = ? = ? = ? = ? ? = 4 x 100 ÷ 12 = 33%? = -4 x 100 ÷ 16 = -25%

The regular price of a CD player is $74. It is on sale for 20% off. Which of the following is closest to the sale price?  A. $40  B. $50  C. $60  D. $70 -20? – = ? – 74 = 74 x -20 ÷ 100 ? – 74 = ? = ? = 59.2

Thirty is twenty percent more than what number? 30 = some number + 20% of that same number. This means that 30 is 120% of the same number. ? = 30 x 100 ÷ 120 = 25 Thirty is twenty percent more than %30 ?100 =

Percent of Change Over Time  An automobile is purchased for $18,000. Its value decreases each year according to the following schedule:  The car’s value decreases by 30% in the first year.  After the first year, its value decreases by 20% each year. What is the value of this car at the end of one year? During which year will the car’s value decrease to less than half its original price?

An automobile is purchased for $18,000. The car’s value decreases by 30% in the first year. What is the value of this car at the end of one year? The car’s values will be $ after the first year. -30? – = ? – = x -30 ÷ 100 ? – = ? = ? =

An automobile is valued at $12,600 after one year. The car’s value decreases by 20% each year after the first When does the car value at half it’s original amount? Half it’s original amount = $ ÷ 2 = $9000 The car’s values will be $ after the second year. -20? – = ? – = x -20 ÷ 100 ? – = ? = ? =

An automobile is valued at $10,080 after two years. The car’s value decreases by 20% each year after the first year. When does the car value at half it’s original amount? The car’s values will be $8064 after the second year. Therefore it is half its value during the third year. -20? – = ? – = x -20 ÷ 100 ? – = ? = ? = 8064

YOUR TURN  An automobile is purchased for $18,000. Its value decreases each year according to the following schedule:  The car’s value decreases by 30% in the first year.  After the first year, its value decreases by 20% each year.  Suppose the value of another car, which also costs $18,000, decreases at the rate of 25% each year. Which car would have the greater value 3 years after it was purchased? Answer: The first car is worth more after 3 years. Car 1 - $8064Car 2 - $7594