Tips 'mental arithmetic' you can't find in textbooks

Have you ever been bored with complicated calculations, tough problems that have to be dealt with on a daily basis? If the answer is yes, don't worry.

Here is a collection of quick calculation methods, extremely interesting mathematical rules, easy to apply in life, and arousing the inspiration of mathematical discovery in each of us.

The multiplication table is a calculation tool that we are all familiar with since elementary school. But perhaps few people noticed that the result of multiplication table 9 formed a very special random rule: the tens and digit units of vertical units would create two opposite numbers from 0 to 9 and from 9 to 0.

One of the common methods to perform multiplication between numbers between 6 and 10 without the multiplication table is: 'Russian-style multiplication'.

Accordingly, you only need to number two hands from 6 to 10 as shown in the figure. Then snap two fingers corresponding to the multiplication to be performed (such as 7 x 8).

Then, take the total number of fingers below the two fingers multiplying by 10, bring the result plus the number of fingers above that we get the result to look for.

The addition method, except for two common fractions, is taught in the case of the denominator and then add (subtract) two numerators for each other.

However, there is little one to notice that, if we draw the calculation process above directly into the calculation, we will have a beautiful and interesting butterfly shape. With this way of doing and drawing, you will never be bored when learning math.

Number one possesses extremely special properties. If you take numbers that include all the digits one by itself, you get the result that an easy-to-remember "forward-back" sequence. For example: 111 x 111 = 12321 or 111.111.111 x 111.111.111 = 12345678987654321.

To quickly calculate the square of any two-digit number that ends in 5, use the following trick: get the tens digit multiplied by that number plus 1, get the result, then write 25 more then we get the right result.

A typical example is the square of 95: 95 ^ 2 = 9 x (9 + 1) & 25 = 9025.

Pi is a great invention in mathematics, but not everyone remembers its true value. At a simple level, just remember that Pi = PIE (the cake) then reverse the letters of this word will be 3.14 - the usual value of Pi number.

More complex, to remember the longer decimal digits of Pi numbers, learn this sentence 'May I have a large container of coffee?' then count the number of letters of each word, we will get 3.1415926.

To quickly multiply two-digit numbers in the range of 10-20, we only need to follow the steps as follows: The first step takes the ones digit of two numbers multiplied by one another.

The second step, take a number plus the ones' place digit of the remaining number, get an extra number 0 after that. Finally, we add the results of these two steps to find the final answer very quickly and not even need to calculate the draft. Example 14 x 13 = 4 x 3 + (14 + 3) 0 = 12 + 170 = 182.

To quickly convert the number of temperatures from Celsius to Fahrenheit, just multiply that number by 2 and add 30 to it. In fact, the results obtained will be more accurate and valuable for practical use because the ability to calculate will be faster.

However, the exact formula of this conversion must be multiplied by 1.8 and then 32.