Using bar modelling to find the best supermarket deal

Speaker: I'm just heading into the supermarket here to grab a few things.

I love cooking, so I'm always having friends and family round for a bite to eat.

But when you add up all the ingredients, it can be quite expensive, so I'm just looking to see what the best deals are to get the best value for my money.

I've always wanted to be a gardener, but I just assumed you wouldn't need to know anything about maths for that.

But since leaving school, I've realised that everyone needs to understand it - and it's great to have a few tricks up your sleeve to help with maths problems.

I did a course at my local FE college and now I have a few simple techniques that have really made this kind of thing a lot easier for me.

Ways to visualise maths problems, like bar diagrams and that seems to really work for me.

Ok, so I'm buying cooking oil and I need to figure out what the best deals are, but it looks like I can get the 3 litre bottle for £4.25, I can get the 2 litre for £2.79, the 1 litre is £1.50 and the 500ml is on offer for 80p.

Speaker: OK, so I'm trying to work out which of these oils is the best value.

Now, I'd normally assume that the biggest bottle was the best value but when there are offers on the smaller sizes, then I'm not so sure.

I need to use maths to figure out the cost price per litre, so I can compare them and to do that I'm going to use my trusty bar diagram.

So let's start with the 3 litre bottle. 3 litres is £4.25.

I need to divide that by 3.

£4.25 divided by 3 gives me 1.41666666, so I can round that up to 1.42. So I've got £1.42 per litre.

So now the 2 litres. So it's 2 litres for £2.79.

OK, so I need to divide that by 2 and that gives me 1.395, so I round that up to 1.40, that's £1.40 per litre.

So now the 1 litre. Well, that's £1.50 so that's an easy one.

I can now easily compare the price per litre of the 3, the 2 and the 1.

Speaker: OK, so I can clearly see the price per litre of these larger bottles now, but its this 500ml bottle that's confusing me a bit because it's on offer.

Now I know that there's 1000 millilitres in a litre, so that means there'll be half a litre in this bottle.

OK, so if half a litre is 80p, which means I need to double the price of this bottle to get the price per litre.

£1.60 per litre. I can now see that the 2 litre bottle is the cheapest price per litre, so, I'll take one of those.

It's good to know you're getting the best deal!