About this video
Sal shows that 46 is 4 tens and 6 ones using blocks. Then he subtracts 4 ones from 46. The tens stay the same and 6 ones minus 4 ones leaves 2 ones, so 46 - 4 = 42.
You'll be able to
- say how many tens and ones are in a 2-digit number.
- subtract ones from a 2-digit number using place value.
- explain why the tens digit stays the same when I take away a few ones.
Key words
- tens place
- The left digit in a 2-digit number; it tells how many groups of ten there are.
- ones place
- The right digit in a 2-digit number; it tells how many single ones there are.
- subtract
- To take away.
Transcript
- So, right here, we have the number 46, we have a four in the tens place, so it literally represents four tens, and we see them here, one, two, three, four tens. That's a ten, that's a ten, that's a ten, and that's a ten. Each of these are ten squares, so all together we have four tens or 40 squares in purple and then we have a six in the ones place.
We have a six in the ones place, we have six ones, and we see that right over here, one, two, three, four, five, six, so we can write that 46, use the same colors, 46 is equal to four tens, four tens and six ones, or I could write plus six ones. Now, let's do something interesting.
Let's subtract, let's subtract four ones from the 46, so, let's think about what it means to take, let's take 46, so I'm going to start with 46, just the number that we have in front of us, and we are going to subtract four. We are going to subtract four. What is this going to be equal to, how many tens?
So it's going to be a certain number of tens, and it's going to be plus a certain number of ones, plus a certain number of ones, so I've left blanks right over here, so how many tens are we going to have? So, 46, that's what we started with, we're subtracting four ones, so we're going to subtract one, two, three, four, we're going to take away four ones.
So how many tens do we have? Well, we still have four tens, so let's write that down, we still have four tens, but now how many ones do we have? Well, now we only have two ones, we only have two ones, and so you see when you have four tens and six ones and you subtracted four ones, well, six ones minus four ones is two ones, and so we get 46, let me do that in the same color, we get 40, I'm having issues here, (laughs) So, it's going to be, this is going to be 46 minus four is equal to four tens, well that's just a four in the tens place, so write a four in the tens place, and then two ones, put a two in the ones place, 42.
46 minus four is 42, and you can see that right there in the ones place, we just took four from this six.
Video © Khan Academy, used under CC BY-NC-SA. Watch on Khan Academy. Puzzicle is not affiliated with Khan Academy.