2.3.2 Calculator Exploration: Decimals and Rounding

In the following exploration, you will learn how to work with decimals on the calculator, and you will revise rounding your answers.

Calculator symbol The calculator can be accessed in the left-hand side bar under Toolkit.

Calculations involving decimals are often more complicated than calculations using just whole numbers, and this is when the calculator is very useful. You enter the decimal point using the button marked Period symbol . You’ll find this below the numbers on the calculator.

On your keyboard, use the period key.

Mathematical OperationCalculator ButtonKeyboard Key
Decimal point
Period key
Period key

Now it’s time to try some calculations. Start with an easy one which you can do in your head:

1.3 plus 2.5

The key sequence is:

Enter this on the calculator and check that you get the answer 3.8.

Activity symbol Activity: Working with Decimals

Use the calculator for these calculations.

(a) 21.74 plus 16.6 minus 19.27

Hint symbol

Discussion

Remember to clear each calculation before you start the next, using the Cancel symbol button.

Solution symbol

Answer

(a)21.74 plus 16.6 minus 19.27 equals 19.07

(b) 31.97 multiplication 0.264

Solution symbol

Answer

(b) 31.97 multiplication 0.264 equals 8.44008

(c) 21.9 division 6.7

Solution symbol

Answer

(c) 21.9 division 6.7 equals 3.26865671641791to 14 decimal places!

In the solution to part (c), you will have noticed that the calculator gave the answer in fraction format before converting it to a decimal. Don’t worry about this at the moment; it will be explained in Unit 7.

The calculator also displayed 14 decimal places in the answer. There are more digits after this, but 14 digits are more than enough for most purposes! In fact, 14 are usually too many, and so we round the answer to give a shorter, more useful form.

For example, if we were to round the displayed answer to 2 d.p., then we would look at the third decimal place, which is 8, to make our decision. Because 8 is larger than 5, it indicates that we would need to round up, giving us 3.27 as a rounded answer.

2.3.1 How Far is It?

2.3.3 More Practice Rounding