FORMULA
Percent of Value = Value
x 100
Total Value
Understanding the percentage
statement:
Example
What is 20% of 75?
-> 100% has value of 75, what is the value
when the percent is 20?
Step1: Circle/Underline
Keyword [20% of 75(-> 100%)]
Step2: Draw/Write
Formula. Required [percent]?
‘Fill in’ given
values
Percent of value = Value x
100
Total Value
20
= Value
100 75
Step3: Solve
20
= Value
100 75
Value = 20
x 75
100
= 15
1% Method
Step1: 100% = 75
Step 2: Find 1 % -> 1% = 75/100 = 7.5
Step 3: Multiply 1% with the required number: 20% -> 20 x 7.5 = 15
Example
There are 35 pupils in the class. 40% of the
pupils are boys. How many boys are there in the class?
Step1: Circle/Underline
Keyword [35 pupil (Total value), 40% boy – How many
boys]
Step2: Write
Formula. Required [value ]? ‘Fill in’ given values
Percent of value = Value x 100
Total Value
40
= Value x 100
35
Step3: Solve
40
= Value
35
Value = 40
x 35
100
= 14
Method 2:
1% -> 35/10 = 3.5
40% -> 3.5 x 40 = 14
Example
Express 20 cm as a percentage of 2.5m
[*** Notes: Units of
measurements must be the same]
Step1: Circle/Underline
Keyword [20cm: value, 2.5m = total]
Step2: Draw/Write
Formula. Required [percent]?
‘Fill in’ values
% of value = Value
x 100
Total
Value
2.5 m = 2.5 x100 = 250cm
% of value = 20
250
Step3: Solve
Percent of value = 20
x 100
250
= 8%
Example
Express $1.85 as a percentage of 50 cents
$1.85 = 185 cents
Step1: Circle/Underline
Keyword [$1.85: value, Total:50ct]
Step2: Draw/Write
Formula. Required [percent ]?
‘Fill in’ given
values
% value = Value x 100
Total Value
% value = 185
50
Step3: Solve
% value = 185 x 100
50
= 370%
Example
The receipt below shows the items that Jane
bought. Part of the receipt was torn.
(a) What percentage of the total amount was
spent on the T-shirt?
(b) 30% of the total amount was spent on the
shoes. How much money did Jane spend on the shoes?
(a) What percentage of the total
amount was spent on the T-shirt?
Step1: Circle/Underline
Keyword
Step2: Write
Formula. What is required [percent]?
and ‘fill in’
given values
% value = Value
x 100
Total Value
% value = 12.15
x 100
81
Step3: Solve
Percent of value = 12.15
x 100
81
= 15%
(2) 30%
of total bill on shoes. How much spend on shoes?
Step1: Circle/Underline
Keyword
Step2: Write
Formula. What is required [$value]?
and ‘fill in’
given values
% value = Value x 100
Total Value
30 = Value
x 100
81
Step3: Solve
Value = 30 x 81
100
= $24.30
DISCOUNT(Reduction/Decrease)
Discount is the reduced rate/amount received based on a usual price or an original price.
Terminology
Cost/Usual/Original Price: The price before any ‘action (discount)’. This price is usually
associated with 100%.
Selling Price: The price that the shop is
selling to the customer; what the customer paid for the goods.
Discount: Price after a discount is
given on the Original Price
Formula: Discount = Original Price – Selling Price
Formula
Discount = Original Price x Percent Discount
(or
can be an amount stated in the word problems, Read sentence!!!)
Example:
The usual price of a sofa is $490. A discount of
20% is given during the Great Singapore Sale. What is the selling price
now?
Formula: Discount = Original Price – Selling Price
Discount
= Discount Percent x Original Price
Method
Step1: Circle/underline keywords. Link given values
(a)
$490 -> usual price -> 100%
Step2: Write
Formula. Link given values: Required value: Selling Price
Given: 20% discount; original Price = $490
Discount
= $490 x 20% = $98
Discount
= Original Price –Selling Price
Step3: Solve
$98
= $490 – Selling Price
Selling
Price = $490 - $98
=
$392
INTEREST
· Interest is usually the
amount of money given by banks to those who deposit money for a period of time.
· Interest may be charged for
money borrowed or loans taken
Terminology
(1) Deposit: Money placed with the bank (usually as
100%)
(2) Interest rate: Interest percent for the deposit
for 1 year (usually)
(3) Interest: Money received after placing Deposit in
the bank
Formula
Interest = Deposit
x interest rate
100
Example
Sally deposited $15 000 in ABC Bank. The
annual interest rate is 2%. Find the amount of interest he would receive
after saving his money with the bank for a year.
Step1: Circle/underline keywords. [deposit = $15000, rate = 2%]
Step2: Write
Formula. Link given values: Required value: Interest
Interest = Deposit x interest rate
100
Step3: Solve
Interest
= $15000 x 2 / 100
= $200
Example
Benny borrowed $60 000 from a bank to buy a new
car. He had to pay 4% interest for 5 years. How much interest did Benny pay?
Step1: Circle/underline keywords. [borrowed = $60000, rate = 4%, 5 years]
Step2: Write
Formula. Link given values: Required value: Interest for 6 years
Step3: Solve
Interest
= $60000 x 4 / 100 x 5
= $12000
PERCENT (BEFORE/AFTER comparison)
Example
Linda salary was 30% less than her husband’s salary. After Mrs Lim had a pay raise of 10%, she earned $460 less than her husband. Find Mrs Lim’s new salary.
Method
There are 2 parts to the question: Before and After a Pay Raise and 2 Persons: Linda and her husband
Step1: Circle/Underline Keywords.
Step2: Link the values. Draw the Before and After diagram
Before: Compared to husband as 100%
10% pay rise = 10% of 70% = 7%
Linda’s new pay is equal to 77% of her husband pay
She earns $460 less than her husband
-> 23% of her pay is $460
% value = Value x 100
Total Value
23% = 460 x 100
Total Value
Step3: Solve
Total Value = 460 x 100
23
= $2000
Linda Pay is $2000 - $460 = $1540
~~~~ END ~~~~ :)
