GCSE Maths: How to Calculate Best Buys
Introduction
What you need to know
Quite often when you go shopping you will generally see similar items or the same item in different sized packaging. For instance washing powder can come in a variety of sizes, but how can you determine which is the best value for money?
Nowadays many supermarkets will include on the shelf how much a particular item will cost for every litre, kilogram or every 100 grams. This will then allow you to make a comparison to similar items that you may be purchasing.
In this article we are going to explore how to calculate best buys and you will see there is always more than one way to do these types of questions.
How To Calculate Best Buys - Example
Example
Take a look at the following question. With all these types of questions you are literally asking how to calculate best buys? Because there is always more than one method to do a question.
Now the aim here is to find a suitable comparison. There is no right or wrong comparison but as long as the comparison is valid then you can determine which shop will offer the best value for money.
One option is to find the cost of 1 tub of yogurt from each shop.
Food Mart: 5 tubs costs £1.80, so the cost of 1 tub can be done by division i.e. £1.80 ÷ 5 = £0.36.
Jim’s: 3 tubs cost £1.05, so the cost of 1 tub can be done by division i.e. £1.05 ÷ 3 = £0.35
So you can see from these calculations that purchasing a 3 pack of yogurt is actually better value for money because each tub costs £0.35 (35p).
There is another way that could have also been used.
Remember the aim to have a suitable comparison.
Suppose you bought 3 packs of yogurts from Food Mart, so this would be a total of 15 yogurt tubs at a cost of £1.80 x 3 = £5.40
And from Jim’s, suppose you bought 5 packs of yogurts, again giving a total of 15 tubs at a cost of £1.05 x 5 = £5.25.
Again you can see that Jim’s offers the best value and this was found by making a suitable comparison on what is being offered.
How To Calculate Best Buys - Example
How to calculate best buys question
What makes this question a little more difficult than the previous question is the fact that there are decimals involved but this should not put you off.
Remember the aim is to be able to find a suitable comparison between the cost of potatoes in both shops.
Here the cost of 1kg of potatoes will be found in both shops and if in doubt always find the value of 1kg in this instance (and similarly for other units).
But how do you ensure you are getting the calculation right? Is it 9 ÷ 12.5 or 12.5 ÷ 9?
For the farm shop a 12.5kg bag costs £9.
If the following block is 12.5kg:
Then if the block is split into 12.5 pieces, how many of these pieces will equate to £9? So the calculation that needs to be done is £9 ÷ 12.5kg = £0.72. This means that at the Farm shop each kilogram of potatoes costs £0.72.
Similarly for the supermarket, the cost of 1 kilogram of potatoes is found by £1.83 ÷ 2.5kg = £0.732.
From these numbers you can see that the farm shop offers the best value for money.
Question Practice
Try the following how to calculate best buys question on your own before looking at the solution.
Where is the best deal?
Question Practice Solution
So how did you get on? Hopefully you found the answer to be Morrisons.
Remember you are looking for a suitable comparison and you will notice that there are two types of units, litres and ml’s.
Morrisons: The total amount of litres is 2 x 3 = 6 litres and this all costs £4.50.
Sainbury’s: 24 x330ml = 7, 920ml = 7.92 litres and this all costs £8.85.
Now 7.92litres is not the easiest number to deal with so probably the best comparison is to find the cost per litre at each store.
Morrisons; 1 litre will cost £4.50 ÷ 6 = £0.75/litre
Sainsburys: 1 litre will cost £8.85 ÷ 7.92 = £1.12/litre
From these numbers it is clear to see that Morrisons offers the best deal.
Overall the topic of Best Buys is relevant to both GCSE Foundation and GCSE Higher Papers. The overall concept of looking for a like-for-like comparison is one that students generally find straightforward. However there can be some questions which are more challenging and such questions would generally be found on calculator paper.
A Foundation Paper “Best Buys” question should be generally relatively one that most students should be able to manage. But as always it is always good practice to obtain sufficient levels of practice in this area.
One suitable way of getting a strong development in the area of exam technique and preparation is through attending a 2 or 3 day GCSE Maths Revision Course which are held in Central London.
You will leave feeling much more confident in the topics that are covered and ready to face your summer exams.
Whatever your goals if you need help getting those top grades then just complete the form and we will be in contact within 24 hours.