8.1.11 Calculator Exploration: Using Percentages

Calculator icon The calculator can be accessed on the left-hand side bar under Toolkit.

In the following exploration, you will use the calculator for calculations involving percentages.

Finding a Percentage of a Number

Suppose that residents in a town are asked their views on a proposed development of a wind farm near the town. The local paper says that 450 people voted, with 54% in favor of the proposal, 36% against the proposal and 10% saying that they were undecided. How many people were in favor of the proposal?

To find the number of people who were in favor, you need to find 54% of 450. The calculation is: 54 percent equation left hand side prefix multiplication of 450 equals right hand side 54 divided by 100 multiplication 450.

Enter this into the calculator and you will see:

Sum 54 hundredths in parenthesis multiplied by 450 equals 243

So, 243 people were in favor of the proposal.

The percent key is useful here. Enter Key sequence showing 54 percent multiplied by 450 equals.

The calculator shows:

Sum showing 54 percent multiplied by 450 equals 243

Again, you can see that 243 people were in favor of the proposal.

Activity symbolActivity: Methods for Finding Percentages

Now it’s your turn. Try both methods (first, entering the percentage as a fraction, and second, using the percent key) to find the number of people who were against the proposal. Then find the number of people who were undecided about the proposal. (Try this calculation without using the calculator.)

Hint icon

Comment

For the first method, enter the percentage as a fraction, then multiply by 450. For the second method, enter the percentage followed by the percent key, then multiply by 450.

Solution symbol

Answer

Since 36% of the 450 people were against the proposal, you want to calculate 36% of 450 to find the exact number. Here are the two methods on the calculator.

Sum showing 35 hundredths multiplied by 450 equals 162
36 percent multiplied by 450 = 162

So, 162 people were against the proposal.

You know that 10% of the 450 people were undecided, so you need to find 10% of 450. You should be able to do this calculation without the calculator: 10% is one-tenth, and one-tenth of 450 is 45. So, 45 people were undecided. The calculator should give you the same answer, but do watch for easy calculations that you can do in your head—it’s good practice!

As a check, the three numbers you have calculated should add to 450. The number in favor was 243, the number against was 162 and the number undecided was 45, and these do add to 450.

8.1.10 Which Percent is It?

8.1.12 To Write One Number as a Percentage of Another