1. Simple calculation by using the law of multiplication and distribution.

The most commonly used method in simple calculation is multiplication and distribution law. The law of multiplication and distribution refers to:

ax(b+c)=axb+axc

cx(a-b)=axc-bxc

Example: 1: 38x 10 1, how should we disassemble it? See who is closer to the whole hundred or the whole ten. Of course 10 1 is better. Then we can split 10 1 into 100+ 1.

38X 10 1

=38X( 100+ 1)

=38X 100+38X 1

=3800+38

=3838

Example 2: 47x98, how to disassemble it like this? 98 should be dismantled to make it closer to 100.

47X98

=47X( 100-2)

=47X 100-47X2

=4700-94

=4606

Second, the benchmark method

Find a more eclectic number from a series of numbers to represent all the numbers, and remember that the selection of this number cannot deviate from this series of numbers.

Example:

2072+2052+2062+2042+2083

=(2062 X5)+ 10- 10-20+2 1

= 103 10+ 1

= 103 1 1

Third, the law of additive combination.

By applying the law of addition and association (A+B)+C = A+(B+C), a simpler operation can be obtained by changing the position of the addend.

Example:

5.76+ 13.67+4.24+6.33

=(5.76+4.24)+( 13.67+6.33)

=30

Fourth, split method.

As the name implies, the splitting method is to split a number into several numbers for the convenience of calculation. This requires mastering some "good friends", such as 2 and 5, 4 and 5, 2 and 2.5, 4 and 2.5, 8 and 1.25. Be careful not to change the size of the numbers!

Example:

3.2× 12.5×25

=8×0.4× 12.5×25

=8× 12.5×0.4×25

= 1000

V. Methods of extracting common factors

This method actually uses the law of multiplication and distribution to extract the same factor.

Example:

0.92× 1.4 1+0.92×8.59

=0.92×( 1.4 1+8.59)

=9.2