To subtract 91 from 99, do you need to regroup? Explain
No. 9 - 1 = 8
yes
To subtract 91 from 99, you would need to regroup. Here's a step-by-step explanation:
1. Start by writing down the numbers vertically, with the larger number on top and the smaller number on the bottom:
99
- 91
2. Begin by subtracting the ones place: 9 - 1 = 8. Write down the result underneath the line:
99
- 91
8
3. Now, move to the tens place. Since 9 is smaller than 1, we need to borrow from the hundreds place. In this case, we're borrowing 1 from the 9 in the hundreds place, which leaves 8 in the hundreds place:
8 (borrowed)
99
- 91
8
4. Add the borrowed 10 to the tens place of the number we're subtracting (91 + 10 = 101):
8 (borrowed)
99
- 91
8
5. Subtract the tens place: 8 - 0 (since we borrowed the 1) = 8. Write down the result underneath the line:
8 (borrowed)
99
- 91
8
6. Finally, subtract the hundreds place: 8 - 9 = -1. Write down the result underneath the line:
8 (borrowed)
99
- 91
-1
So, the answer to 99 - 91 is -1.
To determine whether regrouping is necessary when subtracting 91 from 99, we first need to write down the numbers vertically, aligning them by place value:
```
99
- 91
```
We start subtracting from the rightmost place value column (the ones place). In this case, 9 - 1 equals 8, so we write down 8 underneath the line:
```
99
- 91
-----
8
```
Next, we move to the next place value column (the tens place). Here, we need to subtract 1 from 9. However, when subtracting 1 from 9, we need to regroup. Regrouping involves "borrowing" a ten from the next higher place value column. So we take a ten from the hundreds place column and add it to the tens place column; now we have 8 tens instead of 7:
```
99
- 91
-----
8
```
Now, we can proceed with the subtraction. We subtract 1 from the new value in the tens place (8 - 1 = 7), and write down 7 underneath the line:
```
99
- 91
-----
78
```
Since there are no more place value columns left, we have completed the subtraction. The result of subtracting 91 from 99 is 78.
In summary, when subtracting 91 from 99, we needed to regroup once because we needed to subtract 1 from 9 in the tens place and that required borrowing a ten from the hundreds place.