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Current time:0:00Total duration:4:43

Video transcript

hello in this video we're going to think about techniques for subtracting three digit numbers so let's say we wanted to figure out what 357 minus 156 is pause this video and see if you can somehow figure this out and I don't have to be able to because we're going to walk work through it together but doesn't hurt to try a little bit alright now let's do it together and one way to think about it is what if we were to break up the hundred and fifty-six into its different place values so we view it as one hundred and fifty and six so then this could be re-written as 357 minus 100 minus 100 minus 50 minus 50 that's five tens right there and then minus six now does this help us pause this video and see if you can figure out what this would be well many of you probably said alright if I have three hundred and fifty seven and if I were to take away 100 well then I'm going to be left with 257 and then if I take 50 away from that 250 away from 257 well I have five tens here and I'm going to take away five tens so I'm gonna be left with zero tens I'm gonna be left with two hundred and seven and then if I took two hundred seven and I subtracted 6 from that so two hundred seven minus six that of course is going to be equal to two hundred and one I just took away those six ones and I had seven ones on top of the two hundreds before to get us to 201 so this is one very good technique for being able to subtract numbers and it doesn't just apply to three-digit numbers you can do this with many digit numbers but there's other things that you could be doing you could for example try to adjust the numbers to make the subtraction easier for example you could say hey wouldn't it be nice if instead of subtracting a hundred fifty-six I only had to subtract 150 and there is a way that you could do that as long as whatever you add or subtract to one of these numbers you do to the other then the difference will be the same so there is a situation where you subtract 6 from both of these numbers before you try to find the difference let me write this out so let's say you'd wanted to subtract 6 from both what would this be well 357 minus 6 well we're just going to take 6 ones away from the seven ones here so it's going to be 351 minus 156 minus 6 well that just gets us to 150 and this might be for many of y'all a little bit more straightforward to compute you might realize all right if I have three hundreds and I take away one of those hundreds I get two hundreds if I have five tens and if I take away those five tens I'm going to be left with zero tens and if I have one one and if I take away no one's I'm still gonna have one one or you could say look 300 minus 100 is 250 one minus 50 is just one so that was pretty helpful another technique is to instead of going 150 you might say well what if I wanted to subtract 160 well in that situation you could add four to both of these numbers add four to both what would happen then pause this video and try to figure that out well what's 357 plus four 357 plus three guess this to 360 plus another one gets us to 361 and if I add four to 156 that is 160 and since I added 4 to both I added the same amount to both the difference is going to be the same and so if you look through this 300 minus 100 is 200 it's left and then 61 minus 60s us - that gets us to 201 and what I just kind of did in my head if I wanted to write it out we could say this is the same thing as 361 minus 100 minus 100 and I could break it out completely like I did up here or I could break it out partially I could just break out the hundreds place and then break out the 60 so minus 60 I guess you could view that as I broke out the tens and I didn't write the ones but you can see three and sixty one minus a hundred would be 261 and then you take 60 away from that once again you would be left with two hundred and one so the big takeaway here is there's many different ways to approach subtraction with however many digits you have and this just gets you a glimpse of different methods and some will be more convenient in different situations depending on what numbers you are dealing with