SIMPLE PROBLEM ON PERCENTAGE AND OPEN SENTENCE

Back to: Mathematics Primary 5

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Percentage means one hundredth. The word “per cent” actually mean “per hundred” in Latin. The symbol for percent is %. Therefore, 1% means 1/100 or one hundredth and 7% means 7/100 or seven hundredth. A percent can be expressed as a Decimal or a Fractions

A half pizza can be written as:

1. Percentage = 50%
2. As a decimal = 0.5
3. As a fraction = ½

 

To change numbers (whole numbers, decimal numbers and fractions) to percentage, we just multiply by 100.

CHANGING FRACTIONS TO PERCENTAGE

Exanmple:

Change the following fractions to percentage:

1. 1

Solution

1. 1 = change the mixed fraction to improper fraction.

=

Now multiply by 100.

=

=

= 125%

Multiply by 100.

=

=

= 80%

CHANGING DECIMALS TO PERCENTAGE

To change decimals to percentage, we also multiply by 100 or move the decimal point two times forward.

Example:

Change the following decimals to percentage:

1. 653
2. 758
3. 023
4. 4

Solution

1. 653

Multiply by 100 by moving the decimal point two times forward.

= 1.653  100

= 165.3%

2. 758

Multiply by 100 by moving the decimal point two times forward.

= 0.758  100

= 75.8%

3. 023

Multiply by 100 by moving the decimal point two times forward.

= 0.023  100

= 2.3%

4. 4

Multiply by 100 by moving the decimal point two times forward.

= 0.4  100

= 40%

PERCENTAGE OF QUANTITIES AND NUMBERS

Example:

1. Calculate 25% of 80.

Solution

25% of 80

=

=

= 20

2. If only 10 out of 200 apples are bad, what percent is that?

Solution

Total apples = 200

Bad apples = 10

Fraction of bad apples =

Percentage of bad apples =

=

= 5%

3. 15% of 200 apples are bad. How many apples are bad?

Solution

Total apples = 200

Bad apples = 15% of 200

= 

=

= 30 apples

30 apples are bad

 

PERCENTAGE PROBLEMS

EXAMPLES

1. 25 people were absent in a class of 125 students. What is the percentage of those present?

Solution

Total students = 125

Number of students absent = 25

Number of student present = 125 – 25 = 100

Percentage of students present =

=

= 80%

2^nd method

Total students = 125

Number of  students that are absent = 25

Percentage of students absent =

=

= 20%

Therefore, percentage of students present = 100 -20

= 80%

2. What percentage of 250 is 50?

Solution

This question is the same as finding what percentage of 250 the figure 50 is.

=

=

= 20%

OPEN SENTENCE

An open sentence is a mathematical statement showing two equal expression and containing a missing quantity to be found. This missing quantity is usually represented by a empty box, a blank line or letter x. An open sentence in math means that it uses variables, meaning that it is not known whether or not the mathematical sentence is true or false.

Example:

65-32

=33

94-35

=59

30÷6

Quiz

1. A worker spent 75% of his salary on food.
2. What fraction of the salary was for food?
3. What percentage of the salary is left for other things?
4. The total mark in an English test is 20. Mary scored 75%. What are her score in the test?
5. At the sewing store, Lindsey bought a bag of mixed buttons. The bag included 25 buttons of which 20% were large. How many large buttons did Lindsey get?
6. What percent of 270 is 90?
7. In a basket of 288 oranges, 36 are bad. What percent are good?

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