In preparation for the maths festival you are asked to work out how much water the drinks area will need for the event. the arena buys drinks in 200 litre containers. each person is expected to drink 0.5 litre of water. the arena expects approximately 7,000 people to attend. estimate how many containers of water the arena will need to buy for the event?

We want to know how many people use a 200 liter container. To do that, we do (size of container)/(amount of water people drink)=200/0.5=400 people/container. Next, since we have 1 container / 400 people (1 container = 400 people, so it can go either way) , we want to find how many containers we need for 7000 people. To cross the amount of people out, we multiply the expression by 7000 people to get 7000 containers/400=2.5 containers.