UK Secondary (7-11)
Use a calculator for decimal computation
Lesson

You may or may not have used a calculator before. A calculator is a special tool we can use to help us solve calculations that may be tricky to solve in our heads. In particular, we are going to focus on numbers with decimals.

First, let's get familiar with the decimal point button. It looks like a full stop key.

Now let's watch a video and see how we enter equations into a calculator.

Discussion

Why don't calculators display zeros and the end of decimals?

E.g. Why does the calculator show $3.4$3.4 not $3.40$3.40?

(Watch the video again if you're not sure)

So you can see we just press each button one after the other.

## Careful Calculations

Even though calculators are amazing, they are still just machines. They won't necessarily pick up if you've typed something incorrectly. So it's still really important to understand the maths behind what you're doing so you can make sure you the answer the calculator gives you is reasonable.  This may include the 4 main operations (addition, subtraction, multiplication and division), as well as the order of operations.

For example, try the following calculation on your calculator.  Type it in exactly from left to right.

$6+3\times7$6+3×7

Some calculators will display $63$63, and others will display the correct answer of $27$27.  This is because some calculators can correctly identify that, following the order of operations, the multiplication needs to be completed before the addition of $6$6

Let's try some examples now.

#### Worked Examples

##### Question 1

Consider $11.59\div4.44$11.59÷​4.44

1. Estimate the answer by rounding both values to the nearest whole number.

2. Use a calculator to evaluate $11.59\div4.44$11.59÷​4.44 and write the answer below. Give your answer to two decimal places.

3. What is the difference between the estimate and the actual answer?

##### Question 2

Consider $7.38\times8.12$7.38×8.12

1. Estimate the answer by rounding both values to the nearest whole number.

2. Use a calculator to evaluate $7.38\times8.12$7.38×8.12 and write the answer below. Give the complete decimal answer.

3. What is the difference between the estimate and the actual answer?