It is used to calculate the product between two numbers. In particular, it seems more difficult to multiply two digits by three digits, and multiplication is considered as one of the most basic mathematical operations, and the calculation speed is also slow. For those who want to finish the calculation faster, learning some fast algorithms can improve the calculation speed, which is also the content to be introduced in this paper.
Two-digit multiplication speed algorithms can be roughly divided into two types: one is to decompose the multiplier into two parts, and then multiply them with the multiplicand respectively and add them in the knot; The other is to multiply each bit of the multiplier with the multiplicand respectively, and then add these results.
Let's look at the method of dividing the multiplier into two parts. For example, if we calculate 235x56, we can divide 56 into 50 and 6 and multiply them by 235 respectively, that is, 50x235 =11750.6x235 =1410. Add the two results and finally get the result of 65438+.
Mathematical speed algorithm refers to the calculation method of fast addition, subtraction, multiplication and division by using the special relationship between numbers. Mathematical quick calculation methods are divided into Jinhua quick calculation, Wei quick calculation, historical quick calculation and "swallowing gold in the sleeve" created by the ancients.
Wei's quick calculation allows learners to master the quick calculation method of addition, subtraction, multiplication and division of any number quickly and accurately in a short time with an idea and a method without any calculation tools. So as to quickly improve learners' quick calculation ability in oral and mental arithmetic.
1, quickly add:
The method of calculating the quick addition of arbitrary numbers is very simple. Learners only need to memorize a general formula of quick addition-the quick addition of any digit from high to low, which can be solved by adding the digit to the radix, subtracting and adding the complement, and then adding 1 to the previous digit.
2, fast calculation of subtraction:
The fast subtraction for calculating any number of digits is also a general formula for fast subtraction-"Standard subtraction can completely solve the problem of calculating any number of digits from high to low by adding and subtracting borrowings and subtracting one from the previous digit."
3, multiplication speed calculation:
The general formula of Wei's multiplication is: ab× CD = (a+1)× c× 100+b× d+Wei's fast calculation evolution number ×10. The first method is used to calculate the transition number =(a-c)×d+(b+d- 10)×c, which is suitable for fast calculation of multiplication operations with the same beginning and end of any two-digit number, such as 26×28, 47×48 and 87×84. It is clear that the number of transitions is equal to "8" and "20" respectively.
The second fast calculation method =(a+b- 10)×c+(d-c)×a is suitable for the fast calculation of any two-digit multiplication with the sum of two digits of one factor close to "10" and the difference of two digits of another factor close to "0".
For example: 28 × 67, 47 × 98, 73×88- and so on, and the evolution number can also be clearly equal to "2", 5, 0 respectively. Using the third method to calculate the evolution number = a× d-'b' (complement )× c is suitable for the multiplication of any two-digit number.
Wei's mental arithmetic story when he was a child.
Wei was brilliant since he was a child, and there were many unknown legends in primary school. One day, a math teacher didn't know where to learn that Xiao Wei Wu De was very talented in the speed of digital calculation. In order to be confirmed, he personally worked out an arithmetic problem of 1+2+3+4+ 1000, and asked Xiao Wei Wu De to work out an accurate answer within half an hour.
As a result, Xiao Wei Wu De gave the correct answer in less than five minutes: "500500". Hearing this, the teacher was dumbfounded at once. He can't believe that Wei Dewei has such a fast calculation speed.