Division Algorithm: Answers with decimals

[One speaker] 

[Video opens to a white canvas that the speaker writes on to explain concepts and work examples. 17 divided by 4 is written on the canvas.]

Narrator: In this video we’ll demonstrate how to find the answer to a division problem when the answer is not a whole number, or in other words, when our answer is a decimal number.  

Let’s start out with this problem, seventeen divided by five. From our multiplication table we know that five times three is fifteen, and five times four is twenty. [equations appear] So, seventeen divided by five is going to be somewhere between three and for, but it’s not exactly three and four. [shows a number line with the area between 3 and 4 highlighted] We’re going to get something of an answer with a decimal in it. Now, again, if you have learned a different method to solve division problems like this that works for you, go ahead and use that. We’re not testing on the method that you use, there are lots of methods out there, but I’m just going to demonstrate this one method that you can use if you would like.

We start out the way we did before, creating our little box, putting seventeen under the box, and then divided by five. [draws a long division “box” and puts 17 under it and 5 outside] We start doing the same process of the division algorithm as demonstrated before. Five, five does not go into one, so we move onto the next number. Five goes into seventeen, we know that three times five is fifteen. [writes a 3 above the 7 in 17] So three times five is close to seventeen, but still smaller than seventeen, fifteen. [writes 15 under the 17] Now we subtract. Seven minus five is two, one minus one is zero, [subtracts and gets 2] you can bring the zero down but we don’t need to. Now, this means that seventeen divided by five is three, with two pieces remaining. So now we have to figure out how to put that into decimal form. So right here we put the decimal, [puts decimal after the 3] and then seventeen is the same as seventeen point zero. [puts a decimal point and a zero after the 17] So if we put a zero here we can bring this zero down and keep doing the algorithm as we did it before, [writes a zero after the remaining 2] bring down the zero. Well, five goes into twenty four times. [writes a 4 after the decimal point following the 3] Four times five is twenty. [writes a 20 under the 20 she created from the remaining 2] Now we subtract, we get zero. [subtracts and gets a zero] Zero minus zero is zero, two minus two is zero. So we realize we are done, our answer is the decimal three point four. As we estimated at the beginning, we knew that our answer would be somewhere between three and four, [draws a number line with 3 on one end and 4 on the other and our answer is actually about here [draws a dot on the number line closer to the 3] at three point four. [draws an arrow from the answer, 3.4, to the dot on the number line]

[End of video]