Just mention of Math means trouble and tension for some people, especially kids. Here we bring 9 fast math tricks to really speed up your arithmetic calculations. Knowledge of these math tricks will help you do calculations in your head really fast and more importantly, reduce your fear of math. But most of the math is about practice. So in the article, we have also shared links some really cool practice resources that you can use.
So let us get out our magic stick and pull out some fast math from our math hat. The speed with which you will be able to perform will seem nothing short of magic to others.
Fast math trick 1: Power multiplication or square of a number that ends in 5
Here the speed would really amaze you. Try finding the square of 85 in your head. How much time did it take you? Now try this fast math trick here.
- Ignore 5 in the units place
- Take the digit in the tens place i.e. 8 and multiply it with its successor i.e. 8+1 = 9. The result is 72
- Simply place 25 at the end of the result i.e. 7225. Thats it. 7225 is the square of 85. That is your answer.
Wasn't that fast math trick? This math trick can be used anytime you have to find square of a number ending in 5. It works with 3 digit numbers too. So the square of 135 is ..... first multiply 13 with its successor i.e. 14 = 182. Now add 25 at the end. Your answer is 18225.
Speed in multiplication is all about knowing multiplication tables and facts. Try this multiplication board game to master tables. In our tests with school students, it has proven to be very effective in improving practice and building recall.
Fast math trick 2: Multiplying with 11
How do you multiply a number with 11? Let us take an example. Say you have to multiply 35 with 11. Just follow these 3 steps given below.
- Write 35 as 3( )5 (where ( ) is a space for a new digit that will be inserted in the middle)
- Find the middle digit as 3 (3+5) 5. The middle digit is the sum of first 2 digits
- The number is 385. As simple and as fast as that.
But what if the sum of first 2 digits if more than 9 i.e. a 2 digit number? Let us take an example again. Say the number is 59 that has to multiplied with 11
- Write 59 as 5( )9
- Find the middle digit as 5(5+9)9 = 5(14)9. Since the middle digit is not actually a digit but a 2 digit number, so add 10 to first digit and retain 4 in the middle
- The number is 5+1 (4) 9 = 649. As fast as that
Fast math trick 3: Multiplying with 5
To multiply any number with 5 is same as multiplying it with 10 and dividing it by 2. Right? We can use this rule to speed up our multiplication with 5. So here is the trick. Say you want to multiply 236 with 5.
- Divide the number by 2 i.e. 118
- Now add 0 at the end. The answer is 1180
Was that fast math or what! But wait, what if the answer is in decimal? The rule still holds. Try and multiply 1305 with 5
- Divide the number by 2 i.e. 652.5
- Now multiply it by 10 i.e. 6525. This is same as adding a 0 at the end or moving a decimal point one step to the right.
Fast math trick 4: Multiplying with 9
Suppose you want to multiply a number by 9, is there a fast way? Well, there is something that will help when you are dealing with large numbers and especially if you are fast with subtraction. Say you have to multiply 81 with 9.
- At 0 at the end of the number i.e. 810
- Subtract original number from the new number i.e. 810 - 81 = 729
This rule works every time. The only thing is that it gets a little cumbersome when you are dealing with mid sized numbers say a 4 digit number or so. But this math trick will still make multiplication with 9 faster and less error prone for most of us. So that was our fast math trick for multiplication with 9
Tricks are OK and they help. But the main focus should be practice. Practice these math techniques till numbers begin to pop out of your head, something like the image below. The more you practice, the faster you get and more interested you get.
Fast math trick 5: Multiplying with 25
What if you have you to multiply a two digit number with 25. Say you have to multiply 57 with 25. Can you do the math fast? Can you do it in your head without reaching out for a pen and paper? We teach you the fast math trick to do this calculation in your head
- Add two 0 at the end of the number i.e. 5700
- Now find the half of this number i.e. divide it by 2. So you get 2850
- Divide it again by 2 i.e. get its half. 1425. This is your answer. i.e. 1425 is the product of 57 and 25. Don't believe me, check your calculator.
This will work for large numbers too and will be as effective. So try it with 185. Find the product of 185 and 25
- Add two 0s at the end. So 18500
- Now divide it by 2. So you get 9250
- Divide it again by 2. So you get 4625. That is your answer.
Quick and can be easily done in your head. So that was another fast math trick. Hungry to find more ways to speed up your arithmetic calculations? Keep reading.
Fast math trick 6: Divide by 5
Enough of multiplication tricks. What if you have to divide by 5. Say you want to divide 565 by 5. Just follow this 2 step math trick.
- Double the number i.e. multiply it by 2. So you get 1130
- Now move decimal point one step to the left i.e. reduce one 0. So the answer is 113.
This works with any number, even decimal numbers. So try it with 142.3
- Double up the number. So you get 284.6
- Now move the decimal point to the left by 1 position. So you get 28.46. That is your answer
One of the ways to boost your calculations is to boost your familiarity with numbers. Again, a good fun way we found was this math strategy game that was sent to us for trial. The game involved a lot of thinking. Though makers say that it should be age 7 and up, we recommend it for 9 years to adults. If you like thinking games, this is one that you should try.
Fast math trick 7: Subtracting from 1000
What if you have to subtract a number from 1000? Say the number is 739. There are a lot of carry overs involved and so it is not really that easy to do it in your head. But may be this nifty little math trick will help to speed up your calculations and accuracy. Try and tell me if it was fast for you.
- Subtract the digits in units position from 10 and subtract the digit in hundred's position from 9. That is your answer. So here we have 9-7, 9-3, 10-9. So the answer is 261. That is it. This is only one step.
So that was fast, one step subtraction trick. This, math trick for subtraction works for any number like 10, 100, 1000, 10000, 100000 and so on. Just subtract all the digits from 10 and the last digit i.e. the digit with largest place value from 9. That is your answer.
Fast math trick 8: Multiplying by 15
What is 15? Remember, 15 is 10 + half of 10. So if you to have to multiply any number with 15, this trick or simple math rule will help improve your arithmetic computation speed. Say you have to find the product of 67 with 15.
- Write 0 at the end of the number. Here we have 670
- Divide this by 2. So we have 335
- Add up the 2 numbers i.e. 335+670 = 1005
Fast math trick 9: Fast addition of 2 digit numbers
What if you have to add 67 and 24. Can you do it in your head? Can you do it fast? Try this arithmetic trick and see if it helps in your calculations.
- Add the numbers in the TENs place. i.e. 6+2 = 8
- Now bring one of the numbers in the UNITs place behind 8. Say we bring in 7. So your number is 87.
- Now count up from 87 by 4 i.e. the other number in the UNIT's place. So you up 4 places from 87 i.e. 88, 89, 90 and 91. 91 is your answer.
Let us try this again. Add 75 and 89.
- Add the numbers in the TENs place. We get 7+8 = 15
- Bring in one of the numbers in the UNITs place. We get 159.
- Count up 5 places from 159. So the answer is 160, 161, 162, 163 and 164. Your answer is 164.
This trick is especially helpful for young kids who are learning 2 digit addition in their class. It will help them do their math a lot quicker and hence get them more interested in math. Again, the most reliable and generic way to boost addition is to practice more mental calculations. We found this really amazing addition game. In one game session, we practiced about 60-75 addition problems and it was a huge amount of fun for us and the kids.
The thing to know and understand is that these 'tricks' are really nothing but application of basic mathematical rules. For example, multiplication with 9 is like multiplication by (10-1) which means multiply by 10 and subtract the number from itself etc. If you have some more math tricks up your sleeve, you can share them below. We will include the best ones in this blog with your name in it. Who knows, it might help a lot of people do their math faster and better. Ultimately, the secret to fast math is practice. Practice your math skills, avoid using calculators and you will see your skills improve.
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