4.3Percnet of a Number

1. 4.3Percnet of a Number Parkland 2012-2013

2. Use Mental Math to Find the Percent of a Number

3. Show You Know

4. Calculate the Percent of a Number • A survey showed ¼% of 800 students use inline skates to get to school. How many students skate to school?

5. 30 ¾ % of 400 students surveyed said they own a cell phone How many students own a cell Phone?

6. You have $40.12 in a savings plan. At the end of 1 year you will have 120% of what you started with. How much money will you have at the end of 1Year.?

7. Show you know

8. Remember you can always use proportions or decimals

9. Using a Proportion • Set up a proportion that uses the percent over 100. • Cross multiply to write an equation. • Solve the equation. To set up your proportion, think, “IS over OF equals PERCENT over 100.”

10. Example – What is 20% of 30? x 20 part = 30 100 whole 100x = 30(20) 100x = 600 100 100 x 6 =

11. Using a Decimal • Change the percent to a decimal. • Multiply that decimal by the number you are finding the percent of.

12. Example – What is 18% of 70? 18% = 0.18 0.18 x 70 = 12.6

13. 3. a. There is a discount of 25% off on a $60 pair of shoes. How much are the shoes? $45 $60 x .25 300 120 $15.00 $60 - 15 d. Why is forty-five dollars correct? $45

14. 4. a. A shirt cost $30 plus 7% tax. What is the total cost? $32.10 $30 x .07 $2.10 $30.00 + 2.10 $32.10 d. Why is thirty-two dollars and ten cents correct?

15. 5. a. A $300 bike is on sale. How much is the cost? $225 $300 x .25 1500 60 $75.00 $300 - 75 d. Why is two hundred twenty-five dollars correct? $225