The 11 Times Trick in maths

We all know the trick when multiplying by ten – add 0 to the end of the number, but did you know there is an equally easy trick for multiplying a two digit number by 11? This is it:
Take the original number and imagine a space between the two digits (in this example we will use 52:
5_2
Now add the two numbers together and put them in the middle:
5_(5+2)_2
That is it – you have the answer: 572.
If the numbers in the middle add up to a 2 digit number, just insert the second number and add 1 to the first:
9_(9+9)_9
(9+1)_8_9
10_8_9
1089 – It works every time.

Trick To Convert Fahrenheit and Celsius

Formula :-

To Convert Celsius to Fahrenheit 

°C  x  9/5 + 32 = °F  OR °F = (1.8 x °C) + 32

To Convert Fahrenheit to Celsius

 

(°F  -  32)  x  5/9 = °C OR °C = (°F - 32) / 1.8

Trick To Convert Celsius to Fahrenheit :

You will not get the accurate value of Fahrenheit using this trick.

Step 1 :  Double the celsius

Step 2 : Add 30

For example 

lets take 15 °C

Step 1 :  Double the celsius 15 x 2 = 30

Step 2 : Add 30 so 30 + 30 = 60°F

So it is quite near to the actual answer 59°F

Now to convert  Fahrenheit to Celsius 

Step 1 : Subtract  30

Step 2 : Divide by 2

Mathematics Tips and Tricks

Divide by 5

It's often more convenient instead to multiply first by 2 and then divide by 10.
For example,
1375/5 = 2750/10 = 275.

Addition of Two Numbers: 
     2166
   9327
    -------
Let's add these two numbers in our heads (i.e., without paper). Can you do that?
Our first attempt is to do it like most of us do on paper: 6+7=3 carry the 1 (13), 1+6+2=9, 1+3=4, 2+9=11. The answer is . . . now what were those numbers? The problem here is memory, not mental arithmetic. That's why people use paper (or an abacus, or their fingers), to help out their memories.
Memory is why speed arithmetic experts (I call them "arithmetickers") usually add numbers like these from left to right. It is a little more complicated that way (you have to back track). But, you end up saying the answer from left to right, just as it is normally said.

It is easier to remember a number from left to right.

Let's try again: 2+9=11, 1+3=4, 6+2=8, 6+7=3 and that previous 8 should have been a 9 (because of the carry). I actually remembered the answer, 11493, that time. It's still a test of my memory, but not bad. It may take you a little practice to be able to do that.
Great!!
Isn’t it!


Addition of Columns:

      29

    37

    15

    21

    32

    85

    44

   ---

How about this addition problem?

Add these up in your head. It's not too tough to add up the right column, remember the carry, and add up the left column, just as you would do with a pencil.

In the right column, a speed arithmetic person might group the 9 and the 1 (10), the two 5's (10), and then the 7+2+4 (13) to get 33. Something similar works for the left column. A few people group elevens instead of tens.

Instead, what I do is add 29+37=66, then 66+15=81, then 81+21=102, 102+32=134, 134+85=219, and 219+44=263.
Isn't that slower?
Maybe!

But I have little to remember, just the sum so far. It becomes very fast, if you practice doing it that way. That is how a person with an abacus could do it. And an abacus is just a way of remembering the latest sum. That's something you can easily do without an abacus.


Addendum (Tricks):




Older speed arithmetic books dwelt almost exclusively on tricks. Here are some of those tricks (which you can deduce on your own, instead of memorizing this table):  
Multiply by 5: Multiply by 10 and divide by 2.  
Multiply by 6: Sometimes multiplying by 3 and 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: There is no easy trick method. Multiply by 3 and add 10 times original number.  
Multiply by 14: Multiply by 7 and then multiply by 2 (or vice versa, whichever seems easier).  
Multiply by 15: Multiply by 10 and add 5 times the original number, as above.  
Multiply by 16: You can double four times, if you want to. Or you can multiply by 8 and then by 2.  
Multiply by 17: There is no easy trick method. Multiply by 7 and add 10 times original number.  
Multiply by 18: Multiply by 20 and subtract twice the original number (which is obvious from the first step).  
Multiply by 19: Multiply by 20 and subtract the original number.  
Multiply by 24: Multiply by 8 and then multiply by 3. A similar method works for other numbers that can be factored, like 32 or 45 or many others.  
Multiply by 27: Multiply by 30 and subtract 3 times the original number (which is obvious from the first step).  
Multiply by 45: Multiply by 50 and subtract 5 times the original number (which is obvious from the first step).  
Multiply by 90: Multiply by 9 (as above) 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 a lot more tricks for multiplication, division (divide by 5 by multiplying by 2 and dividing by 10), addition, subtraction, and squaring.

Square Roots


Square a two-digit number that ends in 5 (like 85) by multiplying the left digit by the next highest number (8x9=72), and tack on "25" on the right (7225)

10 Easy Arithmetic Tricks

Math can be terrifying for many people. This list will hopefully improve your general knowledge of mathematical tricks and your speed when you need to do math in your head.

1. The 11 Times Trick
We all know the trick when multiplying by ten – add 0 to the end of the number, but did you know there is an equally easy trick for multiplying a two digit number by 11? This is it:
Take the original number and imagine a space between the two digits (in this example we will use 52:
5_2
Now add the two numbers together and put them in the middle:
5_(5+2)_2
That is it – you have the answer: 572.
If the numbers in the middle add up to a 2 digit number, just insert the second number and add 1 to the first:
9_(9+9)_9
(9+1)_8_9
10_8_9
1089 – It works every time.
2. Quick Square
If you need to square a 2 digit number ending in 5, you can do so very easily with this trick. Mulitply the first digit by itself + 1, and put 25 on the end. That is all!
25² = (2x(2+1)) & 25
2 x 3 = 6
625
3. Multiply by 5
Most people memorize the 5 times tables very easily, but when you get in to larger numbers it gets more complex – or does it? This trick is super easy.
Take any number, then divide it by 2 (in other words, halve the number). If the result is whole, add a 0 at the end. If it is not, ignore the remainder and add a 5 at the end. It works everytime:
2682 x 5 = (2682 / 2) & 5 or 0
2682 / 2 = 1341 (whole number so add 0)
13410
Let’s try another:
5887 x 5
2943.5 (fractional number (ignore remainder, add 5)
29435

4. Multiply by 9
This one is simple – to multiple any number between 1 and 9 by 9 hold both hands in front of your face – drop the finger that corresponds to the number you are multiplying (for example 9×3 – drop your third finger) – count the fingers before the dropped finger (in the case of 9×3 it is 2) then count the numbers after (in this case 7) – the answer is 27.
5. Multiply by 4
This is a very simple trick which may appear obvious to some, but to others it is not. The trick is to simply multiply by two, then multiply by two again:
58 x 4 = (58 x 2) + (58 x 2) = (116) + (116) = 232

6. Calculate a Tip
If you need to leave a 15% tip, here is the easy way to do it. Work out 10% (divide the number by 10) – then add that number to half its value and you have your answer:
15% of $25 = (10% of 25) + ((10% of 25) / 2)
$2.50 + $1.25 = $3.75
7. Tough Multiplication
If you have a large number to multiply and one of the numbers is even, you can easily subdivide to get to the answer:
32 x 125, is the same as:
16 x 250 is the same as:
8 x 500 is the same as:
4 x 1000 = 4,000

8. Dividing by 5
Dividing a large number by five is actually very simple. All you do is multiply by 2 and move the decimal point:
195 / 5
Step1: 195 * 2 = 390
Step2: Move the decimal: 39.0 or just 39
2978 / 5
step 1: 2978 * 2 = 5956
Step2: 595.6
9. Subtracting from 1,000
To subtract a large number from 1,000 you can use this basic rule: subtract all but the last number from 9, then subtract the last number from 10:
1000
-648
step1: subtract 6 from 9 = 3
step2: subtract 4 from 9 = 5
step3: subtract 8 from 10 = 2
answer: 352
10. Assorted Multiplication Rules
Multiply by 5: Multiply by 10 and divide by 2.
Multiply by 6: Sometimes multiplying by 3 and 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 and then multiply by 2
Multiply by 15: Multiply by 10 and add 5 times the original number, as above.
Multiply by 16: You can double four times, if you want to. Or you can multiply by 8 and 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 (which is obvious from the first step).
Multiply by 19: Multiply by 20 and subtract the original number.
Multiply by 24: Multiply by 8 and then multiply by 3.
Multiply by 27: Multiply by 30 and subtract 3 times the original number (which is obvious from the first step).
Multiply by 45: Multiply by 50 and subtract 5 times the original number (which is obvious from the first step).
Multiply by 90: Multiply by 9 (as above) 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.
Bonus: Percentages
Yanni in comment 23 gave an excellent tip for working out percentages, so I have taken the liberty of duplicating it here:
Find 7 % of 300. Sound Difficult?
Percents: First of all you need to understand the word “Percent.” The first part is PER , as in 10 tricks per listverse page. PER = FOR EACH. The second part of the word is CENT, as in 100. Like Century = 100 years. 100 CENTS in 1 dollar… etc. Ok… so PERCENT = For Each 100.
So, it follows that 7 PERCENT of 100, is 7. (7 for each hundred, of only 1 hundred).
8 % of 100 = 8. 35.73% of 100 = 35.73
But how is that useful??
Back to the 7% of 300 question. 7% of the first hundred is 7. 7% of 2nd hundred is also 7, and yep, 7% of the 3rd hundred is also 7. So 7+7+7 = 21.
If 8 % of 100 is 8, it follows that 8% of 50 is half of 8 , or 4.
Break down every number that’s asked into questions of 100, if the number is less then 100, then move the decimal point accordingly.
EXAMPLES:
8%200 = ? 8 + 8 = 16.
8%250 = ? 8 + 8 + 4 = 20.
8%25 = 2.0 (Moving the decimal back).
15%300 = 15+15+15 =45.
15%350 = 15+15+15+7.5 = 52.5
Also it’s usefull to know that you can always flip percents, like 3% of 100 is the same as 100% of 3.
35% of 8 is the same as 8% of 35.

Multiplication Tips and Tricks

Some Tips and Tricks

It is best to put the whole table into your memory using Math Trainer - Multiplication, but here are some tricks that may help you remember your times tables.
Everyone thinks differently, so just ignore any tricks that don't make sense to you.

The Best Trick

Every multiplication has a twin, which may be easier to remember. For example if you forget 8×5, you might remember 5×8. This way, you only have to remember half the table.

Tricks by Number

to multiply by	Trick
2	add the number to itself (example 2×9 = 9+9)
5	The last digit always goes 5,0,5,0,..,
	is always half of 10× (Example: 5x6 = half of 10x6 = half of 60 = 30)
	is half the number times 10 (Example: 5x6 = 10x3 = 30)
6	if you multiply 6 by an even number, they both end in the same digit. Example: 6×2=12, 6×4=24, 6×6=36, etc
9	is 10× the number minus the number. Example: 9×6 = 10×6 - 6 = 60-6 = 54
	The last digit always goes 9,8,7,6, ..
	if you add the answer's digits together, you get 9. Example: 9×5=45 and 4+5=9. (But not with 9×11=99)
10	put a zero after it
11	up to 9x11: just repeat the digit (Example: 4x11 = 44)
	for 10x11 to 18x11: write the sum of the digits between the digits (Example: 15x11 = 1(1+5)5 = 165) Note: this works for any two-digit number, but if the sum of the digits is more than 9, you will have to "carry the one" (Example: 75x11 = 7(7+5)5 = 7(12)5 = 825).
12	is 10× plus 2×

Remembering Squares Can Help

This may not work for you, but it worked for me. I like remembering the squares (where you multiply a number by itself):

1×1=1	2×2=4	3×3=9	4×4=16	5×5=25	6×6=36
7×7=49	8×8=64	9×9=81	10×10=100	11×11=121	12×12=144

And this gives me one more trick. if the numbers you are multiplying are separated by 2 (example 7 and 5), then multiply the number in the middle by itself and subtract one. See this:

5×5 = 25 is just one bigger than 6×4 = 24

6×6 = 36 is just one bigger than 7×5 = 35

7×7 = 49 is just one bigger than 8×6 = 48

8×8 = 64 is just one bigger than 9×7 = 63

etc ...