- Subtracting 1s using place value
- Subtracting 10s using place value
- Subtracting two-digit numbers without regrouping
- Subtracting a 1-digit number with regrouping
- Subtract within 100 using place value blocks
- Addition and subtraction with number lines
- Subtract within 100 using a number line
Subtracting 1s using place value
Sal subtracts 4 from 46 by thinking about place value.
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- When grouping the items by tens and having a remainder at0:30, why does he group them into a group of 6 "ones" instead of 3 groups of "twos", two groups of "threes", or one group of "sixes"?(8 votes)
- For most people, 6 ones is probably easier to understand because when counting objects, people usually count by ones. This is also the reason why 30 in example, is 30. It's 30 ones.(6 votes)
- 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.