9 light mathematical tricks

Many people mathematics can terrify. This list may improve the general knowledge of mathematical methods and accelerate the implementation of mathematical calculations in mind.

1. Multiply by 11
We all know that when multiplied by 10 is added to the number 0, and did you know that there is a simple way to multiply two-digit number by 11? Here it is:
Take the original number and imagine the gap between the two characters (in this example, we use the number 52):
5_2
Now add the two numbers and write them down in the middle:
5_ (5 + 2) _2
Thus, your answer: 572.
If you are adding the numbers in parentheses obtained two-digit number, just remember the second number and add one to the first number:
9_ (9 + 9) _9
(9 + 1) _8_9
10_8_9
1089 - it always fires.

2. Fast squaring
This technique will quickly squared two-digit number that ends in 5. Multiply the first digit on itself one, and at the end append 25. That's all!
252 = (2x (2 + 1)) & 25
2 x 3 = 6
625

3. Multiply by 5
Most people are very easy to remember the multiplication table for 5, but when dealing with large numbers, it becomes more difficult to make. Or not? This technique is incredibly easy.
Take any number, divide by 2 (in other words, divide in half). If the result was an integer attribute the 0 at the end. If not, do not pay attention to the comma and add at the end of 5. It always fires:
2682 x 5 = (2682/2) & 5 or 0
2682/2 = 1341 (integer, so add 0)
13410
Let's try another example:
5887 x 5
2943, 5 (a fractional number, skip comma, add 5)
29435

4. Multiply by 9
It's simple. To multiply any number from 1 to 9 on 9, look at your hands. Fold the finger that corresponds to multiply numbers (eg 9x3 - fold the third finger), count fingers to the thumb bent (in the case of 9x3 - a 2), and then after the count of the folded fingers (in our case - 7). Answer - 27.

5. Multiply by 4
This is a very simple method, although evident only for some. The trick is that you just need to multiply by 2, and then again multiplied by 2:
= 4 x 58 (58 x 2) + (58 x 2) = (116) + (116) = 232

6. Counting tip
If you need to leave a 15% tip, there's an easy way to do it. Calculate 10% (divide the number 10), and then add the resulting number to its half and get an answer:
15% of $ 25 = (10% 25) + ((10% from 25) / 2)
$ 2.50 + $ 1.25 = $ 3.75

7. The complex multiplication
If you need to multiply large numbers, and one of them - even, you can just rearrange them to get an 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. Divide by 5
In fact, sharing a large number of 5 is very simple. All that is needed - simply multiply by 2 and move the comma: 195/5
Step 1: 195 * 2 = 390
Step2: commas: 39, 0, or just 39.
2978/5
Step1: 2978 * 2 = 5956
Step2: 595, 6

9. Subtraction 1000
To perform a subtraction of 1000 can use this simple rule: Subtract 9 from all the numbers except the last. And the last digit, subtract 10 from 1000
-648
Step 1: 9, subtract 6 = 3
Step2: 9 subtract 4 = 5
Step 3: 10 subtract 8 = 2
Answer: 352