Durham College - Decimals - Multiplication - Sals tutorial

Welcome to the Student Academic Learning Services video on multiplying decimals. In this video we're going to look at some examples on the method used to multiply decimal numbers together. For the purposes of multiplying decimal numbers together I'm going to explain the method as I go through the example, as I feel it's the best way to kind of show the actual methods. So, we're going to multiply these numbers the way we normally would, and then at the end we're going to insert our decimal place, and I'll show you how to do that. So we have 4.67 times 0.41, so we're going to multiply these two numbers together, 1 times 7 is 7, 1 times 6 is 6, 1 times 4 is 4, nothing out of the ordinary yet. 4 times 7 is 28, carry the 2. 4 times 6 is 24, plus the 2 is 26, and 4 times 4 is 16 plus that 2 is 18. So we're just multiplying the numbers together, just the way we've been doing them for years. 7 plus 0 is 7, 6 plus 8 is 14, carry the 1, 4 plus 6 is 10 plus that 1 is 11, we're going to carry that 1, you get 9, and we're left with 1. So now we're left with apparently 19,147, but we know that answer's not correct, we have to put the decimal point in somewhere. The way to figure that out is, count up how many numbers are after the decimal places in our original question. So, we have one, two numbers there, and one, two numbers there, two and two is four. So we're going to move the decimal place one, two, three, four places. We're left with an answer of 1.9147. Moving on to the second example, 17.04 times 3.2. Again, 2 times 4, we're just going to take this 2 and multiply it first, that gives us 8, 0, 7 times 2 is 14. That's 2 plus the 1 is 3. 3 times 4 is 12, that's going to give us 1. 3 times 7 is 21, that should be a 2 there. 1 times 3 is 3, plus the 2 is 5. So now we're just going to add these up again, and we have one, two, three places to move, so, one, two, three. Lastly, the last example, 2.005 times 6, 6 times 5 is 30, 6 times 0 is 0, and 6 times 2 is 12. And again we have one, two, three places after the decimal, no decimal point in our number 6 here, so we just put our decimal point in there. So we get an answer of 12.030, or 12.03. If you're a little confused at this, the zeros can be added forever, you could add zeros all the way across the page if you want, that won't actually change the number. The only time it will change the number is if there's a number to the right of all these zeros. And then you can't just add zeros. But, we can just drop the original 0 that we had in our question and all these zeros and just leave it as 12.03. That concludes our video on multiplying decimal numbers. If you have any problems with this material, I encourage you to come to the SALS centre located in room 204 of the Student Services Building and make an appointment to speak with the appropriate learning skills advisor. Thanks for watching.