# Do Quick Calculations With Mental Shortcuts

Even in an age where everyone has a calculator application on their mobile phone it's a handy trick to be able to calculate in your head. Use these calculation shortcuts to crunch numbers with ease.

Photo by jekert qwapo.

Over at the Wired How-To Wiki they've started a list of shortcuts and tricks for calculating larger numbers quickly. While some of them are interesting for the sake of dazzling your friends with your CPU-like brain, others are more practical like:

Fives Times: If you have a multiplication of five, then an easy way to find the answer is to half the multiplied number and times by ten.

For example: 24 * 5 = (24 / 2) * 10 = 120

For more shortcuts check out the wiki at the link below. Know a calculation shortcut or two of your own? Let's hear about it in the comments.

Here is my tip for remembering 9 x

9 x 4 = hold down fourth finger. 3 fingers on left + 6 finger on right = 36

9 x 6 = hold down sixth finger. 5 fingers on left and 4 fingers on right = 54

Fixed (something weird going on at Wired, methinks).

The sum of all the digits, in a number divisible by 3, is a multiple of 3.

e.g. 81 : 8+1=9 81/3=27
654: 6+5+4=15 1+5=6 654/3=218

The sum of all the digits, in a number divisible by 6, is a multiple of 3 and is an even number.

The sum of all the digits, in a number divisible by 9, is 9.

WindowsKey+R
calc

quickest way to open calculator

In Win 7 you can drop the R (run command as well). Typing calc into the program search box will do the trick.