Subtracting multi-digit numbers
Current time:0:00Total duration:3:21
- [Instructor] What we're gonna do in this video is figure out what 389,002 minus 76,151 is. Like always, I encourage you to pause the video and try to figure it out on your own. That's the best way to really, even if you're not able to figure out, or if you get a different answer, then when I work through it with you it will really stick in your brain that much more. Alright, now let's work through it together. The way I'm gonna do it is sometimes called the standard method or the standard algorithm, algorithm being a fancy word for a method. What I'm gonna do is first write the 389,002. 389,002. And I'm subtracting 76,151. You notice the first thing that I did is I aligned the digits to the appropriate place value. I put the ones below the ones. The 10s below the 10s, the 100s below the 100s, the 1,000s below the 1,000s, the 10,000s below the 10,000s, so on and so forth. And now we're ready to subtract. So the first thing we might do is well, let's look at the ones place. Here I have two ones, and I'm gonna take away one one. So I'm gonna be left with one one. That was pretty straightforward. But then things get a little bit more difficult when we get to the 10s place. How do I take five 10s from zero 10s? So let me just not think about that for a second, but I have the same problem in the 100s place. How do I take away one 100 from zero 100s? Now when I go to the 1,000s place, I can take away six 1,000s from nine 1,000s, but before I do that what I want to do is regroup so that I don't have zeros here so that I can take away from the 100s and the 10s place. And so what I can do is I can rewrite nine 1,000s, so I'm gonna take away one of those 1,000s, so I'm gonna have eight 1,000s. And I'm gonna regroup it as 10 100s. So this can be that 1,000 would be 10 100s. Now that solves a problem, except for the 10s place. But what I can then do is I could take away one of those 100s so I only have nine 100s now, and I could regroup that extra 100 as 10 10s. So as 10 10s. And now I can keep subtracting. So in the 10s place, 10 10s minus five 10s, is five 10s. I go to the 100s place, nine 100s minus 100 is 800. I go to the 1,000s place. 8,000 minus 6,000 is 2,000. And then I can go to the 10,000s place. This is essentially eight 10,000s, or 80,000 minus 70,000 is going to be 10,000. One 10,000. And then last but not least, I have my three 100,000s. So there you go. We're done. This is 312,851. This is the standard method. I started at the ones place. Sometimes it's good to just do a check to make sure every digit on top in the appropriate place is at least equal to the digit that you're subtracting from it. And so you can do the regrouping ahead of time. But either way, you will end up with a similar process.