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The same procedure can be used to subtract big numbers like those in the first example. All you have to do is write the numbers under each other; ones under ones, tens under tens, hundreds under hundreds, … so that we can overlook everything easily. The biggest number is always on top and the smaller number is then subtracted from it. Then you start at the very right, with the ones, and start subtracting. First you add the numbers that are going to be subtracted in this column. (In our example it is 7+6=13) Then the answer is subtracted from the top number. (In out example=4)
But because we can’t write 4-13, we have to add a ten so that 4 becomes 14. You would have to add even more tens if we had 25 (for example) instead of 13. (we would have to add 3 tens) So that we can remember to move the ten over, we write a 1 in the tens column, left beside it, 2 by the two tens so on and so forth. This “carry-out” is written in the next column and subtracted from it. (In out example it’s in the tens column.) So instead of having just 7+2=9, it’s even 7+9+1=10. In the lowest row you write the answer of each column. (In our first example it would be 14-13, so the answer is 1). This is how you proceed in each column from left to right and at the very end you’ll have the answer. Example: 163 324-65 477-8 126=???? Because the problem is too hard to calculate in your head, we have to write it out.
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