Before learning subtraction with regrouping children are expected to have understood place value well, and be confident subtracting without regrouping.
Subtraction Without Regrouping
When subtracting, we subtract the smaller number from the larger number. While doing this, we first find the difference in the digits in the units place. Then we find the difference of digits in the tens place. In general, subtraction that does not require decimal conversion is much easier when doing this.
Example: 47 -12 = 35
Now let’s take a look at how we did the above subtraction, in order.
Units digit: We subtracted the number with units digit 2 from the number with units digit 7 in the above number and found the result 5. So we will write the number 5 in the units place first.
Tens digit: This time, we subtract the number 1 in the tens place from the number 4 in the tens place. So we write the number 3 in the tens place down.
Subtraction With Regrouping
When subtraction is done, no smaller number comes out of the larger number. For example, we cannot subtract 8 from 5. When performing subtraction with natural numbers, we will apply the operation that requires regrouping. In this direction, tens are taken from the previous digit. The concept of ‘borrowing from the tens column’ is a great help for kids to better understand how to subtract with regrouping. Now let’s make an example on this subject and try to understand how it is done.
Example: 42 – 26 =16
Now, we will examine and learn how we did the subtraction with the natural numbers above, respectively.
Units digit: As we have seen, the number 2 is not substracted from the number 6 in the units digit. So we borrow a 10 from the neighbor in the tens place. So the number 2 becomes the number 12. Then we subtract the number 6 from the number 12 and write the number 6 down.
Tens digit: There is number 4 in the tens digit, but since we gave 1 ten in the units digit, 3 is left here. When we subtract 2 from 3 we have 1 and write 1 in the tens place down.
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