Increase Your Mind Power – Use Mental Math Tricks

After the article on Neurobics this is the second article in the “Increase Your Mind Power” series. Although most people will use a calculator (nearly every cell phone has one), doing math in your head is a really useful skill. And this does not always have to be hard. There are several tricks and shortcuts available to make doing math a lot easier.

The general rule is to always look for the easiest way to do the math. One of the tips is to always look for the numbers that are close to 10 or 100 or 1000. Below are some examples of the tricks you can use.

Update 12/13/2009: if you need more information about mental math, I have made a list of the 7 most popular mental math and speed mathematics books.

Addition
One way to add lots of small numbers is to clump together the ones that add up to multiples of 10. For example, if you have to add 3 + 4 + 5 + 7 + 9 + 11 + 6, that can be arranged as (3 + 7) + (9 + 11) + (4 + 6) + 5 = 10 + 20 + 10 + 5 = 45. This can be really useful when playing dice games like Yahtzee.

Subtraction
A useful trick when subtracting numbers is to begin with the smaller value and mentally skip your way up the difference, with jumping points at recognizable boundaries, such as powers of 10. For example, to subtract 56 from 214 you would start with 56, then add 4 + 40 + 100 + 14 (= 158). Try this once and you see how easy it is.

Multiplying
Suppose you want to multiply 78 x 6. You might immediately think “70 x 6 = 420 and 8 x 6 = 48, and 420 + 48 = 468.” This is one way to quickly arrive at a solution without pen and paper. On paper it would look like this: (70 x 6) + (8 x 6) = 468.

Here is another shortcut for the same problem. See it as (80 x 6) – (2 x 6). The accompanying “internal dialog” might go like this: “80 x 6 = 480, but that is two ‘sixes’ too many, so take away two sixes (12) and I have 468.” There is always more than one way.

More tricks and shortcuts
Other great mental math tricks and shortcuts can be found at listverse.com and betterexplained.com.

Try to create your own math shortcuts, or try any of the tricks and shortcuts you read about and adopt the ones that seem to work best for you. When you find the shortcuts that work easiest, train your brain to use them habitually.

This article was inspired by two great books by Steven Gillman, 100 Ways to Increase Your Mind Power and A Book of Secrets.

Have fun!

Gerber

Related posts:

1. 7 Most Popular Mental Math and Speed Mathematics Books