One of the numbers I missed in the Fast Math – Tips & Tricks post was the number Eight. Now don’t think that I skipped this number because there aren’t any easy shortcuts. Because there sure are!
What you always should think about when you want to make any calculations quickly in your head, is how can you easily simply things. For most people, some calculations will be far easier than others. Find your strong and weak points and use this to your advantage in order to get good at fast math. Multiplying by eight is a perfect example of this.
FAST MATH SHORTCUTS
Now instead of multiplying a number by eight one time, most people will find it far easier to multiply a number by two. After all, multiplying a number by two, is as easy as adding the number to it self.
So instead of multiplying by 8 we will use the number two. Now obviously we wont get the correct result by multiplying by 2, if we are to get the result of a number multiplied by 8. Hence we just multiply several times – three times to be exact.
Lets take an example; we are not to multiply 10 by 8. This is pretty easy as I already showed you that when multiplying by 10, we simply add a zero to the number being multiplied by 10 (which is 8). Hence we add 0 after 8 and we get: 80. But for illustration purposes lets cut it down a bit more:
10 * 2 = 20
20 * 2 = 40
40 * 2 = 80
The result is the same. Now will obviously look extremely easy and probably even more troublesome than simply multiplying by 10. But that’s just because it’s that very number, which makes it easy to illustrate the point.
Say you should multiply 56 by 8. How would you do now? My bet is you can do it in a matter of 2 seconds. However, multiply 56 by 2 is far easier, which is the same for the next and final number.
You should always think in these kind of ways in order to become a fast math expert! Cut things down and find your strong sides in order to make easy and fast mathematical calculations.