# 10 Simple but Useful Math Hacks for Everyday Use Looking for some handy math hacks? Then you've come to the right place. Math isn't everyone's forte but it doesn't need to be over complicated. The following math hacks will dig you out of math hell if you've misplaced your calculator. Here we go... [Image Source: Pixabay]

## Subtraction from 1000 made easy as pie

If you find yourself needing to subtract anything from 1000 this example of math hacks might come in handy. It's pretty simple, to be honest. Subtract all digits from 9 except the last one. And subtract the last digit from 10. Combine the answers in order and you get your answer! Tidy.

1000 - 795 = ?

Split the numbers up and subtract the first few from 9 and the last from 10.

First step = 9 - 7 = 2

Second step  = 9 - 9 = 0

Third step = 10 - 5 = 5

Last step = Then recombine the numbers

1000 - 795 = 205

## Multiplying big numbers made easy

This trick from our list of math hacks could be very useful for you, so long as the numbers are even that is. Take your original sum and halve one side whilst multiplying the other by 2. Repeat until you get to an easier sum you can do in your head.

Let'sets take 32 x 125 for example.

32 x 125 = ? (halve the first number and double the second)

16 x 250 = ? (keep going)

8 x 500 = ? (keep going)

4 x 1000  = 4000

## Easily multiply by 5

Divide any number you want by 2. If the result you get is a whole number then tag a zero onto the end. If not, ignore the decimal and simply add 5 to the end! Got it? Let's take a look.

Let's multiply 35 by 5.

So,

35  x 5 = ?

35  x 5 =(35/2) & 5 or 0

(35/2)  x 5 = 17.5 (this is fraction so ignore the decimal) & 5

35 x 5 = 175

OK how about something a bit more complicated?

Very well lets say 5,887 x 5

5,887 x 5 = ?

(5,887/2) x 5 = 2943.5 (fraction again so ignore the decimal) & 5

5,887 x 5 = 29,435

Nice and simple right? [Image Source: Pixabay]

## Math hacks to multiply by 11

Need to multiply a number by 11? We've got that covered too. Take your number and split it up into individual numbers. If a single number that's simple enough of course. Now separate the numbers apart and add the individual numbers together. Stick this answer between the other two numbers and boom, you get your answer!

Let's use 54 as an example.

54 x 11 = ?

Split the 5 and 4 apart and add them together.

54 x 11 = 5 & (5 + 4) & 4

54 x 11 = 594

## Multiplication by 4 made easy

Do you need to multiply by 4? This is one of the easier math hacks on our list. Take the number you want to multiply by 4. Multiply it by 2 first. Then multiply the product by 2 again! Nice and easy. Let's have a look at an example, shall we?

How about multiplying 4 by, say, 23?

23 x 4 = ?

First step = 23 x 4 = (23 x 2) + (23 x 2) = ?

Last step = 23 x 4 = 46 + 46

Boom! Done and dusted.

## Easily divide by 5 hack

This is another relatively simple hack on our list. If you need to divide by 5 simply double the number in question and then move the decimal point. Let's give you an example:-

195 / 5 = ?

(195 x 2) = ? (ignore the division by 5)

390 (now move the decimal place)

195 / 5 = 39

Cool, nice and easy.

## Easily find the percent of a number

Do you have trouble finding the percent of a number without a calculator? No problem try this hack out. Whatever percentage you need of a number simply divide them both by 10. Then multiply the products together to get your answer? Easy right?

Let's take 40% of 300 for example. Divide both by ten. That'll give you 4 and 30 respectively. Now multiply 4 by 30, or vice versa. Hey presto, 120! Amazing right? Give it a go for yourself.

## Sorting out tips the "easy" way

OK let's jump onto something a little more practical. You've had a lovely meal and you fancy leaving a tip for the staff. How much do you want to leave? Let's say you're feeling generous and want to leave 15% of the bill. First of all, take the bill total and divide it by 10 to get 10%. Then add another half to the result to get your final answer.

Pretty straight forward and you might do this anyway, I know I do! Let's run through an example.

Our bill is \$45 dollars and we want to leave 15% tip so:-

15% of \$45 = ?

First step = 15% of \$45 = (\$45/10) + ((\$45/2) / 2)

Second step = 15% of \$45 = \$4.5 + \$2.25

Third step = 15% of \$45 = \$6.75

Bargain, thanks for that! Now have a nice day and all that! [Image Source: Pixabay]

## Easy peasy quick square root calculation

Our next entry on your list of math hacks will certainly prove very useful! This little trick is great for finding the square root of a two-digit number that ends with 5. To do this trick simply multiply the first digit by itself plus 1. Then you'll need to add, just physically tag, 25 to the end. Eh voila, you get you answer! Neat.

Let's take 35 square for example.

Square root of 35  = 3 x (3+1) & 25

First step =  (3 x 4) & 25

Second step = 12 & 25

## Find the cube root without a calculator

Ok here we go, something a bit more complex. If you want to find the cube root of a number you'll only need to remember the cubes of 1 to 10. You will need to take the last digit of your number, this will be the last digit of the result. Next, you ignore the last three digits. After that, you look at what you have left and find which of the beginning 10 instances of cubes is the closest to the remaining numbers (as a number). Now combine your answers to get the result. Confused? Let's use an example.

Let say you want to find the cube root of 39,304.

Step 1 = Strip the 4 of the end, this is the last digit of your answer.

Step 2 = Now ignore the last three digits, including step 1 above (except for it being the last digit of your answer). This will leave 39.

Step 3 = Now cube the 3 and the 9.

3 x 3 x 3 = 27

9 x 9 x 9= 729

As we are left with 39 from our answer in step 2, 3 cubed is the closest to 39.

Step 4 = Now take the 3 and the 4 and combine (not add) to get your answer. So the cube root of 39,304 is 34! Bingo!

## Easily convert from Celsius to Fahrenheit, and vice versa

Our next math hack is an oldie but a goodie. You may already know this one. To convert from Celsius to Fahrenheit multiply the temperature in Celsius by 2. You'll then need to add 30 to it to get a ballpark figure. For a more precise number multiply by 1.8 and then add 32.

Let have a go, shall we?

Ballpark:-

32 degrees Celsius = ? degrees Fahrenheit

(32 x 2) + 30  = ? Fahrenheit

64 + 30 = ? Fahrenheit

32 degrees Celsius = 94 degrees Fahrenheit

More precise:-

32 degrees Celsius = ? degrees Fahrenheit

(32 x 1.8) + 32  = ? Fahrenheit

57.6 + 32 = ? Fahrenheit

32 degrees Celsius = 89.6 degrees Fahrenheit

Nice, how about in reverse? Well, to do this you'll need to reverse the order above. So for the ballpark figure, you'll subtract 30 and divide by 2.

Ballpark:-

94 degrees Fahrenheit = ? degrees Celsius

(94 - 30) / 2  = ? degrees Celsius

64  /2  = ? degrees Celsius

94 degrees Fahrenheit = 32 degrees Celsius

Precise:-

89.6 degrees Fahrenheit = ? degrees Celsius

(89.4 - 32) / 1.8  = ? degrees Celsius

57.4  /1.8 = ? degrees Celsius

94 degrees Fahrenheit = 32 degrees Celsius (to nearest whole number)

Want some more? There are some great ones in the following video:-

So there you go! Any of these useful? Now if you find yourself without a calculator you can impress your friends with your math hacks skills! Do you have any other examples? Feel free to share them below in the comments.

Sources: BrightSideBigIdeas, FactsVerseArchitectureAndDesign