# Percentages_and_Change_Expressed_as_a_Percent by xiagong0815

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

Warm-Up:
1. If two ratios are ________, they form a proportion.
2.

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            =
a
m    k
f        e
Previous class practice problems
Objective:
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
Vocabulary:

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

Decimals to percentage:                  Fractions to percentage:

.58                                     3
.08                                     4           1
2
.04                                   12                4
.6
25                5
How do you          What percentage of 56 is 42?
find the percent
using the percent
What percentage of 75 is 15?
proportion?

a   p

b 100
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
equation?
A family sells a car to dealership for 60% less than they paid for it.
a=p·b
They paid \$9000 for the car. For what price did they sell the car?

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?

a=p·b

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?
interest?

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
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?
Vocabulary:

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

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

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

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.

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)
Summary:
Wrap-Up:
Vocabulary Review
Test Reminder

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