How To Subtract In Your Head
by Murdo Macleod
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Articles
Published on this site: January 2004 - See
more articles from this month
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.
Murdo Macleod is co-author of the "Fun With Figures"
mental math course, which shows anyone from age 8 and up how
to perform lightning-fast mental calculations. http://FunWithFigures.com/
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