# How To Do Quick Mental Math

Mathematics is an essential part of the Universe. One could even go as far as to say the Universe is mathematics. As such we are introduced to this science when we are but mere children. Its basic facts and rules are drilled into our heads to prepare us for the future. The whole global economy runs on math. But you’re not here for mind-bending formulae of math hitherto unknown to the common man. You’re just here in the hopes to learn how to do your everyday numerical tasks just a bit faster.

Well that is what we’ll be focusing on in this post. After you finish going through the list you still won’t be able to compute algorithms like a computer but you will hopefully have learned how to speed up multiplying in your head. So let’s dive in and talk hard numbers.

## The Cheater’s Multiplication Trick

Totally a name we just came up with, and definitely not something that’ll help you cheat on your next math exam. Still, we felt the need to include this very basic trick on the list. Long story short, if you ever need to multiply a number by 5, and it’s a number you don’t usually deal with, cut it in half and multiply it by 10. Same answer, easier formula. For a very simple example, imagine you have to multiply 50 with 5. You could instead opt for multiplying 25 by 10. You’ll reach the answer – 250 – quicker than the other method.

## The Reverse Percentage Trick

Calculating percentages in your head is a nightmare, and yet it is something you might have to do often. If that is the case, rest easy because the method we’re about to reveal might change your life. Well, at long as you keep it simple. The formula, simply put, is that when you are asked to find a percentage of a value, you can switch the numbers around to help make it easier. For a very simple example consider being asked to find what 2% of 100 is. Switch it around and instead find 100% of 2, which is 2 and is the answer to the first question as well.

## The Approximate Celsius To Fahrenheit Trick

How many times has it been that you’ve had to quickly fire up Google just to convert temperatures between those two annoying measurement units? More times than you can count right? Well there is a way that allows you to do that relatively quickly in your head. Simply take the measurement in Celsius, multiply it by 2, and then add 32 to it. It will be a very close answer. The exact formula requires you to multiply by 1.8 instead of 2 but at that point we’d just take Google’s help.

## Multiplying Double Digits Trick

More often than not you might find yourself in a pickle; quickly counting inside your head as someone waits for a response. The trick to multiplying two double digit numbers quickly is about to be yours. Train yourself to use it automatically and you’ll be spewing out answers like a mathematical rapper. To explain how it works consider having to multiply 12 by 12. Put the two numbers in a matrix, essentially writing one on top of the other. Now multiply the contents of the second column of the matrix, in this case 2 and 2, so 4. “Write” this down in your mind under the answer line.

Now multiply the elements of the matrix diagonally, so 1 with 2 and 2 with 1, and then add the answers of both, in this case 4. “Write” this down as well. If the answer came out in two digits, take a carry. Now simply multiply the elements of the first column, 1 and 1, and add any carried numbers to them and then “write” the answer down. By now it should look like ‘144’, having started backwards from the right. And that is your answer. May take a little time to wrap your head around this method but it’ll be super quick to do once you learn it.

## Simple ‘Divisible By 3’ Check

If for whatever reason you need to check if a number is divisible by 3 there is a very simple way to do so, given the number is not a single digit number of course. For example, if you want to check if 180 is divisible by 3, all you’ve got to do is add the digits of 180 and check if the answer is divisible by 3. So 1 + 8 + 0 = 9, which is divisible by 3, so 180 is divisible by 3 too. It’s a neat little trick that may come in handy some day.

## Quick 15% Tip Calculation

A very simple trick that might not be known to you. If you’re one of those people who always tips 15% at restaurants and has trouble calculating the tip, this might help. Simply put, instead of applying percentage formulas, just take 10% of the total bill. 10% should be much easier to calculate in your head. Once you have that, halve it for the 5% value. Now add both and you’ve got 15% of the total bill. Happy tipping.

## Conclusion

And those were just some quick mental math tricks you can use in your day-to-day life. Let’s hope you remember to use them. In the meantime, if you’re looking for other useful stuff to learn, we’ve got plenty of lists here. You can start with any of them of course, though Useful Windows Shortcuts To Speed Up Your Daily Computer Use and Time-Saving Tips For Moving are great reads.