For the majority of these math tricks, the purpose is to find manageable numbers to work along with inside your head, and stick along with operations that you will be most accustomed to.
Math Trick #1 :
How to multiply a 2 digit number by 11 :
For example, 43×11. Take typically the original number and imagine a space amongst the 2 digits :
4_3
Now add the 2 numbers together then put them inside the middle :
4_ (4+3) _3 that is the same as 4_7_3
The answer… 473
If the numbers inside the middle add up into your 2 digit number, insert the second number and add 1 to the first :
For example, 67×11
6_ (6+7) _7
(6+1) _3_7 that is the same as 7_3_7
The answer… 737
Math Trick #2 :
How to square a 2 digit number ending in 5
If you need to square a 2 digit number ending in 5, multiply the first digit by itself + 1, and put 25 on the end.
For example, 65^2 (which could be written as 65×65)
6x (6+1) or 6×7 = 42
Put a 25 on the end of it…
The answer… 4225
Math Trick #3 :
How to multiply big numbers by 5
Take any number, then divide it by 2. Then…
If typically the result is whole (which is, theres’s no remainder), add a 0 at the end.
If it's not whole, ignore typically the remainder and add a 5 at the end of the number.
For example, 4252×5 = (4252/2) and add a 5 or 0 to the end of the number
4252/2 = 2126 (it’s a full number so add a 0 to the end)
The answer… 21260
Here’s an additional example : 8667×5
Divide the number by 2 : 4333. 5 (there’s a remainder therefore add 5 to the end)
The answer… 43335
Math Trick #4 :
How to multiply by 4
The trick right listed below is to simply multiply by 2, then multiply by 2 once more. Ultimately, you want to work along with smaller numbers which are easier to work along with inside your head.
For example 82 x 4 = (82 x 2) x 2 = (164) * 2 = 328
To multiply by 8, just multiply by 2 one more time (656).
Math Trick # 5
How to multiply by 9, or 99, or 999
Multiplying by 9 is really like multiplying by 10-1.
9×9 is the same as 9x (10-1) and that is (9×10) -9 which is 90-9 or 81.
Let’s attempt a harder example : 56×9 = 56×10-56 = 560-56 = 504
To multiply by 99, it’s the same idea, except you multiply by 100-1.
So, 56×99 = 56x (100-1) = 5600-56 = 5544.
Multiplying by 999 is comparable to multiplying by 9 and by 99, except currently you multiply by 1000-1
22×999 = 22x (1000-1) = (22×1000) – (22×1) = 22000-22 = 21978
Math Trick # 6
Multiplying by doubling and halving
There are cases when you’re multiplying 2 numbers together and one of the numbers is even. In this case you are able to divide which number by 2 and multiply other number by 2. You can do keep doing this till you get numbers which are simple to operate along with inside your head.
Let’s say you desire to multiply 14 by 16. You may double and halve the numbers until you get your answer :
14×16 = 28×8 = 56×4 = 112×2 = 224
Another example : 12×15 = 6×30 = 6×3×10 = 180
Here’s an additional example :
48×17 = 24×34 = 12×68 = 6×136 = 3×272… this could seem large, but you are able to break it down further into :
3×270 + 3×2 = 810 + 6 = 816
Math Trick # 7
Working along with Percentages
Remember that “per cent” is much like saying “parts of one hundred”.
So, it follows that 8 % of 100, is 8. As another example 23.89% is the same as saying “23.89 parts of 100″.
Find 8% of 200.
8% of the first hundred is 8. 8% of the 2nd hundred is also 8. So it follows that 8% of of 200 is 8 + 8 = 16. Therefore 8% of 200 is 16%.
Another bonus trick : you are able to flip percents. For example 35% of 8 is the same as 8% of 35.
Using percents has a very practical application when you’re at a restaurant. Let’s say you desire to leave a tip of 15% on a $50 dinner. You may immediately calculate it inside your head :
15% of $100 is $15, therefore 15% of fifty is half of that, or $7.5
Let’s try out one more example : Calculate a 15% tip on a $60 dinner.
Using the very same approach, 15% of $100 is $15, so then 15% of fifty is half of that, or $7. fifty. Also, you know that 15% of $10 is $1.5
So then 15% of 60 is the same as 15% of 50 + 15% of 10… which equals $7.5 + $1.5, or $9. 00.
Math Trick # 8
Quick Addition by using the left-to-right approach (rather than the familiar right-to-left) :
Instead of using a right to left approach, we are able to begin from the left and move to the right. Take the following example :
45 + 34
Usually, you would certainly first sum up 4 to 45, then add 30 to the result. But by using the left to right approach, you first sum up 30 to 45, and then you add 4 to the result. Although this example is very simple, you’ll begin to see the advantages of this technique while you begin to work with it.
If you’re working with 3 digit numbers, the actual procedure is the same.
459 + 637
This example is a little more complicated than the before, yet it’s very easy to solve using the left to right approach. First, start by adding 600 to 459, which results in 1059. Now the problem is simplified to 1059 + 37. You simplify it even further by adding 30 to 1059, and after that adding 7 to the result… that's 1096.
Math Trick # 9
Subtracting a big number from 1000.
To subtract a big number from 1000 you are able to use this basic rule : subtract all but the last number from 9 (taking the absolute value… that is, ignoring if the number is negative), then subtract the last number from 10 :
1000 - 736
Step 1 : subtract 7 from 9 = 2
Step 2 : subtract 3 from 9 = 6
Step 3 : subtract 6 from 10 = 4
Your answer : 264
Math Trick # 10
Multiplication rules…
Multiply by 5 : Multiply by 10 and divide by 2
Multiply by 6 : Multiplying by 3 then 2 is easy
Multiply by 9 : Multiply by 10 and subtract the original number
Multiply by 12 : Multiply by 10 and add twice the original number
Multiply by 13 : Multiply by 3 and add 10 times original number
Multiply by 14 : Multiply by 7 then multiply by 2
Multiply by 15 : Multiply by 10 and add 5 times the original number
Multiply by 16 : You can double four times or multiply by 8 then by 2
Multiply by 17 : Multiply by 7 and add 10 times original number
Multiply by 18 : Multiply by 20 and subtract twice the original number
Multiply by 19 : Multiply by 20 and subtract the original number
Multiply by 24 : Multiply by 8 then multiply by 3
Multiply by 27 : Multiply by 30 and subtract 3 times the original number
Multiply by 45 : Multiply by 50 and subtract 5 times the original number
Multiply by 90 : Multiply by 9 and put a zero on the right
Multiply by 98 : Multiply by 100 and subtract twice the original number
Multiply by 99 : Multiply by 100 and subtract the original number
There are also another math Tricks software that is more attractive :), unfortunately it is still in Android Application, download here or here. Have Fun :)
0 comments:
Post a Comment