Early math review
Subtracting 3-digit numbers (no regrouping)
Sal shows how to subtract 357-251 with place value.
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We have the number 357. So the three is in the hundreds place. So that represents three hundreds: one hundred, two hundred, three hundreds. Three hundreds right over here, that's what this three represents, 'cause it's in the hundreds place. Let me write that. This is the hundreds place. Then we have a five in the tens place. So that represents one, two, three, four, five tens. Five tens. And then last but not least we have, in the ones place, we have seven. So that represents seven ones: one, two, three, four, five, six, seven. Seven ones. Now from that, we want to subtract 251; or, we want to subtract two hundreds, five tens, and one one. So pause this video and think about what that is going to be. So let's work through this together. Let's first focus on the ones. We're starting off with seven ones in three hundreds, five tens, and seven ones. 357. Seven ones. And we are going to take away one one right over here. Let me do this in a different color. So we're gonna take away one one. So let's take away one one. And then we're gonna be left with six ones. Now let's go to the tens place. We start with five tens, but we're going to take away, we're going to subtract, five tens. So let's subtract one ten, two tens, three tens, four tens, five tens. We've taken all of the tens away. So now, we have zero tens. And then finally, we started with three hundreds but we want to take away two of them. We want to take away two of the hundreds. So let's do that; let's take away one hundred and two hundred. And we're just going to be left with this hundred right over here. We're going to be left with one hundred. Three hundreds minus two hundreds is one hundred. So hopefully this gives you an appreciation of what's happening in place value. You could just say, "Oh, I'll line up the numbers, "and I'll look at the place values, and then "over here I have a seven minus one is a six, "a five minus five is a zero, a three minus two is a one," but I really want you to think about what's going on. This is seven ones minus one one, which gives us six ones; this is five tens minus five tens, so you're not gonna have any tens left over, so it's zero tens; and three hundreds, three groups of a hundred, minus two groups of a hundred is gonna leave us only one group of a hundred. So we're gonna be left with 106: one hundred, zero tens, and six ones.