Helpful. How quickly assumed in the mind Bashny.Net

This list of a few little-known mathematical tricks will show you how to quickly take in mind in cases more complicated than 5 multiplied by 10, and even your friends will be able to use you as a calculator.

1. Multiply by 11
We all know how quickly multiply the number by 10, just need to add a zero at the end, but did you know that there is a chip as easily multiply two-digit number by 11?
Suppose we need to multiply 63 by 11. Take the two-digit number, which must be multiplied by 11 and submit it between two figures place:
6_3
Now fold the first and second digits of this number and put it in this place:
6_ (6 + 3) _3
And our result of the multiplication is ready:
63 * 11 = 693
If the result of the addition of the first and second digit of two-digit number, just insert the second number and the first digit of the original number is increased by one:
79 * 11 =
7_ (7 + 9) _9
(7 + 1) _6_9
79 * 11 = 869

2. Fast squaring numbers ending in 5
If you need to build to build a kadrat two-digit number ending in 5, then you can make it very simple in my mind. Multiply the first digit of the number to itself plus one and add at the end of 25, and that's it:
45 * 4 = 45 * (1 + 4) = 2025 _25

3. Multiply by 5
For most people, the multiplication by 5 it is easy for small numbers, but how quickly assumed in the mind large numbers multiplied by 5?
You need to take that number and divide by 2. If the result is an integer, then add it to 0 at the end, if not, drop the remainder and add a 5 at the end:
1248 * 5 = (1248/2) _ (0 or 5) = 624_ (0 or 5) = 6240 (the result of dividing by 2 is an integer)
4469 * 5 = (4469/2) _ (0 or 5) = (2234.5) _ (0 or 5) = 22345 (the result of dividing by the number 2 with a remainder)

4. Multiply by 4
It is very simple and, at first glance, the obvious feature multiplying any number by 4, but shall behold it is people do not realize it at the right time. To simply multiply any number by 4, you need to unozhit it by 2, and then again multiplied by 2:
67 * 4 = 67 * 2 * 2 * 2 = 134 = 268

5. Calculate 15%
If you need to mentally calculate 15% of any number, that is an easy way to do it. Take 10% of the number (dividing the number 10), and add to that number by half received 10%.
15% of the 884 rubles = (10% of 884 rubles) + ((10% of 884 rubles) / 2) = 88.4 + 44.2 ruble ruble = 132.6 rubles

6. Multiplication of large numbers
If you need to multiply large numbers in his mind, and one of them even, then you can use the method to simplify the factors, even reduce the number twice, and the second is increasing twice:
32 * 125 is
16 * 250 is
8 * 500 is
4 * 1000 = 4000

7. Divide by 5
Divide large number 5 in the head is very simple. All you have to do is multiply the number by 2 and move the comma one character ago:
175/5
Multiply by 2: 175 * 2 = 350
Is shifted by one character: 35.0 or 35
1244/5
Multiply by 2: 1244 * 2 = 2488
Is shifted by one character: 248.8

8. Subtract 1000
To subtract a large number of thousands, follow a simple technique takes away all the digits of the number 9, except the last, and the last digit of the number, subtract from 10:
1000-489 = (9-4) _ (9-8) _ (10-9) = 511
Of course, to learn quickly take in mind, you need a lot of time to practice using these techniques to bring them to automatism, a one-time reading will leave only zeros in your head.