 Let's do another example. I heard an American talk about the extremely high prices of petrol recently so I thought let's try and figure out whether it's cheaper or more expensive than it is in Australia. So I just looked up the price of petrol in the USA and on average right now it's $2.23 US dollars per gallon. Okay now I don't personally know how much a US dollar is worth in an Australian dollar so I have to look that up and I don't personally know how big a gallon is so I have to look that up and when I do I can write them in as conversions and I do it the same way I did it the last time by multiplying by one. So I want the gallon on the top so it cancels with the gallon on the bottom and one gallon it turns out is worth 3.785 litres and I also want to convert the US dollars to Australian dollars and this time I'm going to want the US dollar on the bottom so it cancels with the US dollar on the top and it turns out that's equal to 1.34 Australian dollars and now we see we can cancel the US dollars we can cancel the gallons and we end up with Australian dollars per litre and all we've done is we've multiplied by one because a gallon is exactly equal to 3.785 litres and we've multiplied by one again because one dollar 34 in Australian is equal to a one dollar US and so we end up with 2.23 times 1.34 divided by 3.785 and our final unit is Australian dollars per litre which is the unit I'm used to seeing on petrol pumps so I'll be able to understand whether that's a big or a small number so I plug that into a calculator or do my arithmetic in my head and I get 78.9 cents per litre which I must say does look like a small number to me.