Percentages
1
Contents
1.1 Percentages
1.2 Percentage Change
1.3 Profit and Loss
1.4 Discount
1.5 Interest
Mr. Bloom, Monroe H.S.
1.1 Percentages
A percentage is a fraction converted to a decimal, and then multiplied
by 100 and add percent sign (%).
7
For example, 7% 
100
Example 1
Change each of the following into percentage.
(a) 0.83
Solution :
(a) 0.83  0.83 100%  83%


(b)
12 12

 .48100%  48%
25 25
(b)
12
25
1.2 Percentage Change
When an original value is changed to a new value, the
percentage change of the value can be measured in
the following way.
New value  Original value
Percentage change 
100%
Original Value
1.2 Percentage Change
Example 2
Peter’s weight decreases from 60 kg to 48 kg. Find the
percentage change of his weight.
Solution :
Percentage change 
48  60
 100%
60
 20%

Percentage decrease of weight is 20%.
If the answer is positive, it
means a percentage increase.
If the answer is negative, it
means a percentage
decrease.
1.3 Profit and Loss
The profit and loss in trading refers to the difference between
the cost price and the selling price.
(1) Percentage change 
New price  Original price
100%
Original price
The selling price can be found if the cost price and
the percentage change are given.
(2) Selling price  Cost price (1  Profit percentage) or
Cost price(1  Loss percentage)
1.3 Profit and Loss
Example
4
David bought a car 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?
Solution :
54 000  90 000
100%
90 000
 40%
Percentage change 

Loss percentage of car’s price is 40%.
When the percentage
change is positive, it means
there is a profit.
When the percentage
change is negative, it means
there is a loss.
1.4 Discount
Discount is a price deduction from a marked price in
purchasing.
(1) Percentage change 
Marked price  Selling price
 100%
Marked price
(2) Selling price  Marked price (1 Discount percentage)

Example
5
The marked price of a washing machine is $4500. If the
selling price is $3000, find the discount percentage.
Solution :
4500  3000
The discount rate 
 100%
4500
1
 33 %
3
1.5 Interest
Let P be the principal, I be the interest, A be the amount, r% be the
interest rate per period and t be the number of periods.
(a)
Simple Interest
(1) Simple interest I  P  r  t
(2) Total amount A  P  I


1.5 Interest
Let P be the principal, I be the interest, A be the amount, r% be the
interest rate per period and t be the number of periods.
(a)
Simple Interest
(1) Simple interest I  P  r  t
(2) Total amount A  P  I


Roberto deposited $3000 in a savings account for 2 years @ 3% in order to buy a car. How much interest did
he earn?
I = Prt =>
I= P
r
t
=$3000 x .03 (decimal form of 3%) x 2
$90 x 2 = $180 in interest earned