How To Subtract In Your Head

by : Murdo Macleod

We all have to subtract numbers sometimes... whether it's budgeting your household expenses, checking your change at the store, or installing that new shelving unit during a spot of home DIY.

The problem is, you won't always have a calculator handy.

Well fear not.

Doing simple calculations in your head is just as easy and even faster than using a calculator.

Here's a quick way to do basic subtraction without relying on any electronic gadget...

Suppose you offer 50 cents for something costing 18 cents. What's the easiest way to check your change?

50 - 18 = ?

To take 18 from 50, we note that 18 is close to 20, so we take 20 away from 50 (to get 30) and add 2 back on.

Answer: 32

Similarly, in 73 - 49 we decide to take 50 away from 73 and then add 1 back on. We get 24.

Do you see how easy this is? Try these for yourself:

  1. 62 - 36 = ?

  2. 84 - 48 = ?

  3. 71 - 27 = ?

  4. 43 - 16 = ?

  5. 55 - 28 = ?

The above sums are simple. Yet most people would do them the hard way: by working from right-to-left, and trying to remember a "carry digit".

The method you've just learned is based on an ancient formula (or 'sutra') called "By Addition and Subtraction".

It's simple to learn, and after a few practice runs you'll use it instinctively.

A few tips to help you:

  • Always relax when you're doing mental math (or when performing any mental activity for that matter).

  • Never strain your mind - the natural way is best.

  • And remember, you're only ever competing with yourself. Go at the pace that's most comfortable for YOU!

Like most things in life, there's an easy way and an unlimited number of difficult ways.

Be good to yourself and get used to finding the easy way,

Your whole life will run smoother as a result.