Subtraction using Addition

The title of this post might sound a bit ironic to you. But you should note that it is mathematics with which we are dealing here today. And in mathematics, magical things are possible (of course we have to follow some basic rules, duh!).

Subtraction is one of the first things we learn in mathematics. It is also one of the hardest for a beginner. The rule of carry-over spins our head right round, right round. Now also I remember when my father was trying to make me understand how subtraction works. Tears rolling down my cheeks as I try to fathom out the intricate complexities of this weird, new operation.

Anyway, bygone memories aside, today I’ll show you a quick and easy way to perform subtraction. This method can help you effortlessly find the difference between 2 numbers.

So let’s get to it at once by starting with an example : 825-578(Get your pens ready)

First, let’s solve it the more common way. Following shows the traditional way(most probably the way you must’ve been taught as a child) to solve the problem.

Carry over 1 from 2. The 2 now becomes 1 and 5 becomes 15. 15–8 is 7 which is the right-most digit of the answer. Next, carry 1 from 8. 8 becomes 7 and 1 becomes 11. 11–7 is 4 and 7–5 is 2 which makes 825–578=247.

You do reach the result from this method but you have to agree that this method is difficult to calculate in the head. I mean why, in the first step, 2 becomes 1 but 5 becomes 15? Well, there is a logical explanation for that but it’s complicated especially if you’re a kid learning it for the first time.

So now I’ll show you another method to solve the same problem. An easier one, if you will.

The difference between 825–578 is kind of like the number of steps you take from 578 to go to 825, taking 1 step at a time.

So now imagine you’re at 578 and 825 is your destination. Also, there are some milestones along the way. At 600 and 800 to be precise. So first you go from 578 to 600, taking 22 steps. Then you move onto 800 by taking another 200 steps. And you cover the last stretch of distance from 800 to 825 in 25 steps. So the total steps you took are 200 + 22 + 25 which gives us 247.

For me, solving the problem with this method is inherently easier as there are no carry overs in this and subtraction is turned into addition. A small tip: You can also break it down even further like breaking 22 into 20 & 2 for easier calculation. I know this method is a bit longer to explain but it’s super quick when you do it mentally.

Let’s solve another problem using this method. This time using 4 digit numbers, say 7341–2858. The major milestones in this case would be 3000 and 7000. But you’ll can also add other, minor milestones to ease you. For eg. adding the milestones at 2900 and 7300.

So, the total now becomes

See. Quick and as easy as A+B+C. Literally.

And this was it. A simple, straightforward method to solve your subtraction questions, mentally. And it will obviously become easier with some practice.

Bye.