Standard index form is a way of writing either huge numbers or very small numbers into a format that we can apply more easily to our maths. If we consider an example of the Earth's distance relative to the Sun, how far is it between Sun? Well, it is approximately 150 million kilometers. Now, to use this number day-in and day-out could come with its problems in that I could miss count how many zeros I have and therefore my calculations are wrong. Before I show you how to write that in standard form, it's worth considering the basics. 100 can be written as 10 times 10, alternatively, as an easier method, we could write it as 10 squared. Now, as a rule, what I always say is the indicee matches the number of zeros that you need. Now, is this principle that I want you to bear in mind for later on. So going back to my original problem, how do I write 150 million in standard index form? How do I write it in a form which is the same as this but I could more readily use? I could write 150 multiplied by 1 million, but that in itself hasn't solved anything. I still have a number of zeros which I need to record and I could lose track of. Alternatively, I could write 1 million as 10 to the 6, the 6 being indicated by the number of zeros here. Now, there's nothing wrong with that, and indeed, that number does match that. I've not changed how much I've got, but this doesn't appear with the rules of standard index form, which says that this number here has to be between 1 and 10. Taking a step back, I could write 15 times 10 to the...