Percentages_and_Change_Expressed_as_a_Percent by xiagong0815


Date: October 18, 2011
              Topic: Percent and Change Expressed as a percent

                     1. If two ratios are ________, they form a proportion.

                                               13 feet

                                                                        a + 5 feet

                                  8 feet                                              5 feet

                     3. What is wrong with this proportion?       Why? What is the correct proportion?
                              b        c             h        i

                                           d     g                j            =
                                                     m    k
                              f        e
Previous class practice problems
            By the end of class you
            should be able to find a
  percentage, original price, and/or sale price
by using proportions, the percentage equation,
      and/or percentage change equation

Percentage =   A percentage is a fraction in which the denominator is equal to 100.
   %           For example, 7% 

                 Decimals to percentage:                  Fractions to percentage:

                      .58                                     3
                      .08                                     4           1
                            YOUR TURN
                      .04                                   12                4
                                                            25                5
How do you          What percentage of 56 is 42?
find the percent
using the percent
                    What percentage of 75 is 15?

a   p
b 100
                             YOUR TURN
  a = part of

    b = base        1) What percentage of 16 is 10?

    p = percent
                    2) What percentage of 48 is 20?
How do you
                     A dress shirt that normally costs $38.50 is on sale for 30% off.
find the a part
                                    What is the sale price of the shirt?
using the percent
                    A family sells a car to dealership for 60% less than they paid for it.
                    They paid $9000 for the car. For what price did they sell the car?

                                            YOUR TURN
                     3) As you walk into a store you see the skate board you always
                      wanted at a 35% discount from its original price of $39.99.
                                What is the sale price of the skateboard?
How do you
                    125% of what number is 17. 5?
find the base
using the percent
equation?           20% of what number is 80?


                               YOUR TURN
                    4) 60% of what number is 13.5?

                    5) 150% of what number is 34?
How do you                      You deposited $840 in a savings account that earns a simple
                                    interest rate of 4.5% per year. You want to keep the
find simple                                   money in the account for 4 years.
                                              How much interest will you earn?

                               You deposited $125 in a savings account that earns a
                                     simple interest rate of 1.75% per year.
      I = Prt                        You earned a total of $8.75 in interest.
                                 For how long was your money in the account?
I = interest

  P = principal
                                                 YOUR TURN
r = annual interest rate
                                   6) A savings account earns simple interest at
                                              a rate of 6% per year.
t = time in years                Last year the account earned $10.86 in interest.
                           What was the balance in the account at the beginning of last year?

 Percentage                                                               is the ratio of the amount of
  Change                                                             =   change to the original amount .

                           New value  Original value
 Percentage change                                   100%
                                Original Value

                                                                         Peter’s weight decreases from 60
                                                                                    kg to 48 kg.
                                                                         Find the percentage change of his

     If the answer is positive, it means a percentage increase. If
     the answer is negative, it means a percentage decrease.
   7) In one year, the toll for passenger cars
     to use a tunnel rose from $3 to $3.50.
           What was the percent increase?

8) The average monthly precipitation for Chicago, Illinois, peaks in June at
      4.1 in. The average monthly precipitation in December is 2.8 in.
            What is the percent decrease from June to December?
Real Life:
                                  9) David bought a car
      Profit and Loss
                                 for $90,000 three years
                                ago. He sells the car for
                                 $54,000 this year. What
                                    is the percentage
                                change of his car’s price?

 When the percentage
 change is positive, it means
 there is a profit.
 When the percentage
 change is negative, it means
 there is a loss.

                                    Still Your Turn!
Real Life:
      Percent Error

                      Percentage Error  Estimated Value  Actual Value 100%
                                                  Actual Value

                                10) A decorator estimates that a
                             rectangular rug is 5ft by 8ft. The rug is
                             actually 4ft by 8ft. What is the percent
                                  error in the estimated area?
                             A) 0.25%       B) 20%     C) 25%     D) 80%

                                 Yeah, You Know It. It’s Your Turn!
          Independent Practice:

Page 137 Solve It – Getting Ready
Page 148 (8, 16, 17, 18)
Page 149 (28, 39)
Page 150 (42)
Vocabulary Review
Test Reminder

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