About this video
Sal shows that 65 is 6 tens and 5 ones. Then he subtracts 40, which is 4 tens and 0 ones. Taking away 4 tens leaves 2 tens, and the 5 ones stay the same, so 65 - 40 = 25.
You'll be able to
- write a 2-digit number as tens plus ones.
- subtract tens from a 2-digit number using place value.
- explain why the ones digit stays the same when I subtract a multiple of ten.
Key words
- tens place
- The left digit in a 2-digit number; it shows how many groups of ten.
- ones place
- The right digit in a 2-digit number; it shows how many single ones.
- group of ten
- Ten blocks put together, worth 10.
Transcript
- [Voiceover] Right here, we have 65 blocks. And you can count them if you like. But we can represent them with the number 65. By writing a six in the tens place, we're literally saying that we have six tens. And this is a 10, this is a 10, this is another 10, this is another 10, this is a 10, and this is a 10.
We have six groups of ten and that makes 60. And then we have five ones. Five in that orange color. And then we have five ones. And you see them right here. One, two, three, four, five. Now let's do something inter... Well, actually, let me just first write that down again.
Just to emphasize it. We can write down that 65, 65 is equal to six tens, six tens plus five ones. Plus five ones. Now, let's do something interesting. Let's start with 65, so let me write that down again, so we're gonna start with 65. I'm having trouble changing colors.
We're gonna start with 65 and I'm gonna subtract... I'm going to subtract 40. I'm going to subtract 40 from that. What am I really doing here? Well, I'm starting with 65, I'm starting with this, and I'm subtracting four tens and zero ones. Let's subtract four tens from here.
Let's subtract one, two, three, four. I took away four of the tens. How many tens do I have left over? Well, I have left over two tens. This is going to be equal to two tens. And how many ones do I have? Well, I still have five ones. So, I still... I still have five ones.
And that makes sense. I had five ones, I took away zero ones, so I'm still going to have five ones. What is this going to be equal to? We can write 65. 65. Minus 40. Minus 40 is... Let me do the... I want to do the ones in that orange color. Minus 40 is equal to, another way of saying two tens is by putting a two in the tens place, and a...
And then we have five ones. A five in the ones place. Two tens plus five ones, or 25.
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