How to Multiply & Divide Integers

Video Transcript

"Hi I'm Steve Jones and I'm going to tell you how to multiply and divide integers. Well the question is why integers and the answer is they're simple. But first of all with multiplication we know that everybody learns tables up to 12 times 12 and we all know that 12 times 12 is 144. So tables enable us to get up to 12 times 12 but when we get bigger than that we have to use long multiplication for example 163 multiplied by 41. Now there are many different ways of denoting this but what most people do is they usually start with the units column and we know one times 163 is just 163. Now we then need to say well what about the 4, this isn't 4 this is 40 so in fact what we do is we start at the next column 10 bigger to the left and we therefore put a 0 in this column and that represents the 0 of the 40 and then 4 three's are 12 and then 4 sixes are four carrying 125 and four one's are four, five, six, so 6520 and by adding those two columns of figures we end up with a result of 6,683 for 41 multiplied by 163 so that is a simple long multiplication. Obviously if this bottom number gets bigger we get more lines, we get one line for each digit in the multiplier and obviously we get digits in here depending on how long the top number is too but this is a comparatively simple example. For division we have more or less the same thing. The only difference with tables you have got to identify a number that you recognize in your tables for example if you get the number 49 you know 49 is 7 times 7so this is easy. But for long division is the only way to go if you have to divide integers and that will be done. Let's say the same numbers, let's say 163 this time divided by 41. People denote these things in different ways. Make sure you keep your decimal point here and you know that well 4 4's are 16 so this is going to be about 4. 41 goes into 1, no, 16, no, 163, yes it goes 3 times an then you calculate what is left and so forth so long division is quite a routine way of calculating this number. Let's see how it works. We'll put the number at the top three point something so three one's are three, three four's are twelve, so that's 123. We take away what's left and I end up with 40 and I now have to use the number 400 to give me whatever is in here and I'll get 9 and I keep on doing this 9 times 1 is 9 and 9 four's are 36, 369 and this leaves me 39 and so I'll bring another 0 down and I'll get a series of numbers here which gives me the result of my division. So what you've got here is a way obviously long multiplication you get a very big number, long division you are likely to get a number which has a lot of decimal places. Take care it's easy to make a mistake doing it, just keep it simple."