Video: Find the Difference by First Subtracting Hundreds

Look at how Amelia broke apart a number to help her subtract. 456 − 200. First, subtract the hundreds. 400 − 200 = _. Then, add the remaining hundreds to 56 to find 456 − 200.

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Video Transcript

Look at how Amelia broke apart a number to help her subtract. 456 take away 200. First, subtract the hundreds. 400 take away 200 equals what? Then, add the remaining hundreds to 56 to find 456 take away 200.

This problem is all about a method that Amelia uses to subtract two numbers. She’s trying to find the answer to 456 take away 200. And the first thing we’re asked to do is to look at how she breaks apart a number to help her work out the answer.

If we look at Amelia’s calculation, we can see that she’s taking away a number of hundreds, that’s 200, from a three-digit number, 456. Before she broke it apart, we know that Amelia must have modelled her number using base 10 blocks. To make 456, she would have needed four hundreds, five tens, which equals 50, and then six ones. Now, she knows she’s got to subtract 200 from this number, so she’s subtracting a number of hundreds. If we subtract a number of hundreds from a three-digit number, the tens and the ones are going to stay the same.

So, we can see in the diagram what Amelia then does. She takes her four hundreds, and she sets them apart from the rest of her number. These are the four hundreds that she’s going to take the 200 away from. And so, that’s why we can see that she’s broken apart her number into 56 and 400.

She’s done this to make it a lot easier to subtract the hundreds. And we can see that this is exactly what we’re asked to do in the first part of the actual question. First, subtract the hundreds. 400 take away 200. If we start with 400, then take away 100, we’re left with 300. And 300 take away another 100 leaves us with 200. 400 take away 200 equals 200.

Now, although we’ve subtracted 200, we’ve still got a number that’s being broken apart. So, we need to put it back together again. And this is what the last part of the question asks us to do. We’re asked to add the remaining hundreds to 56. This is gonna help us find the answer to 456 take away 200. Instead of four hundreds, we now have two hundreds, and so we need to add 200 to 56. The total is 256.

We used Amelia’s method of breaking apart a three-digit number to help us subtract. We wanted to take away a number of hundreds from a three-digit number, so we separated out those hundreds to help us take away from them. First, we subtracted the hundreds. 400 take away 200 equals 200. Then, all we had to do is to combine the two parts back together again. 456 take away 200 equals 256.

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