What topics does the grouping method apply to? And how to use the grouping method? Let's have a look.
Grouping method:
It is suitable for addition and subtraction mixed operations with certain regularity. Through addition, subtraction and recombination, the original calculation is changed into a smaller number or the same number calculation, which simplifies the calculation process.
Grouping method: Look at symbols and find rules.
(1) Observe the addition and subtraction symbols in front of each number; Please note that the first number is preceded by+.
(2) Dividing periods according to the law of symbols;
(3) Group calculation.
Let's look at a simple example first.
Example1:10-9+8-7+6-5+4-3+2-1=?
First of all, read the topic carefully and observe the law of the topic.
1, the numbers in this question are continuous, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.
2. Consistency-++appears alternately.
Can this special topic be grouped?
Let's look at the title of 1, and the characteristics of-+coincidence are more obvious. Example 1 can also be written as:
+ 10-9+8-7+6-5+4-3+2- 1
Is this more obvious?
The+-symbol is a period, grouped as follows:
+( 10-9)+(8-7)+(6-5)+(4-3)+(2- 1)
The number in each bracket is 1.
= 1+ 1+ 1+ 1+ 1
=5
10-9+8-7+6-5+4-3+2- 1=5
Example 2: 20+19-18+17-16+14+13-12+.
Look at the symbols and find out the rules.
The symbol is++-+-,and the symbol period is+,-
Two numbers are a group, but the first number is the left number. Pay attention to this.
=20+( 19- 18)+( 17- 16)+( 15- 14)+( 13- 12)+( 1 1- 10)
=20+ 1+ 1+ 1+ 1+ 1
=25
Have you learned the clever grouping method?