Subtracting smaller number from greater number

Subtracting smaller number from greater number has always been an easy task for me. Because I always followed this approach:

Subtract the numbers as small minus big and then multiply the result with minus one. This gives me the accurate result and saves me from the hassle of “borrowing” method.

Example – We have to subtract 6526 from 8437. (i.e 6526 – 8437 = -1911).
In this case, I would simply follow these two steps:

  1. 6526 – 8437 = result
  2. final_result = result * -1

But what if I had to do it manually? (using the borrowing method). Manual subtraction gives me this result:

6526 – 8437 = -2089 (which is clearly wrong!)

So what’s going on here? Let’s look at the basics. When I use the borrowing method to subtract these two numbers, the last three digits are positive but the first digit comes out to be negative.

  6 5 2 6
- 8 4 3 7
  x 0 8 9

In this case: 0, 8 and 9 are positive numbers but x is -2 (which is negative).

Once we know that, all we have to do is add (-2000) and (+89). That gives us (-1911). Which is the correct result!

This is something I discovered while doing manual subtraction after a long time. And I found it awesome enough to share it in a blog post 🙂

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