1.9 A note on the four operations
The four operations are addition, subtraction, multiplication and division. You will already be using these in your daily life (whether you realise it or not!). Everyday life requires us to carry out maths all the time – for example, checking you’ve been given the correct change, working out how many packs of cakes you need for the children’s birthday party and splitting the bill in a restaurant.
- Addition (+) is used when you want to find the total, or sum, of two or more amounts.
- Subtraction (−) is used when you want to find the difference between two amounts or how much of something you have left after a quantity is used. For example, if you want to find out how much change you are owed after spending an amount of money.
- Multiplication (×) is also used for totals and sums, but when there is more than one of the same number. For example, if you bought five packs of apples that cost £1.20 each, to find out the total amount of money you would spend the sum would be 5 × £1.20.
- Division (÷) is used when sharing or grouping items. For example, to find out how many doughnuts you can buy with £6 if one doughnut costs £1.50, you would use the sum £6 ÷ £1.50.
Checking calculations
You should always double-check your calculations using an alternative method. There are different methods you can use, and the one you choose will probably depend on the calculation.
One very good way of checking calculations is to carry out a reverse calculation, or an inverse calculation as it was called earlier in this session. This is where you use the opposite type of sum (or opposite operation) to check your answer:
- Addition (+) and subtraction (–) are opposite operations.
- Multiplication (×) and division (÷) are opposite operations.
If your check results in the same answer, it means that your original sum is correct too. For example, you may have made the following calculation:
200 – 168 = 32
A way of checking this would be:
32 + 168 = 200
Alternatively, if you wanted to check the following calculation:
80 × 2 = 160
A way of checking this would be:
160 ÷ 2 = 80
Summary
In this section you have:
- learned how to read, write, order and compare positive numbers
- looked at different ways of using negative numbers in everyday life
- carried out calculations
- learned how to use the inverse method to check answers.