1. rounding method: according to the operation law and operation nature, it can be rounded into integer parts (especially integer ten, integer hundred, etc.). ) to merge or disassemble, and then get the result.

For example: 8+4. 1+ 1+5.9.

=(8+ 1)+(4. 1+5.9)

= 10+ 10

=20

For example: 1.25× 18

= 1.25×( 10+8)

= 1.25× 10+ 1.25×8

= 12.5+ 10

=22.5

For example: 78×98

=78×( 100-2)

=78× 100-78×2

=7800- 156

=7644

2. Change method: appropriately change the operation method, that is, add instead of subtract, subtract instead of add, multiply instead of divide, and divide instead of multiply; Or change the operation order, or simplify it by reduction, addition and subtraction.

For example: 4.7 × 0.25+7.3 ÷ 4

=(4.7+7.3)×0.25

=3

For example: 3 ÷ 4-0.5 ÷ 0.7-0.3 ÷ 0.4+5 ÷ 7.

=(3÷4-0.3÷0.4)+(5÷7-0.5÷0.7)

=0

The role of simple calculation:

1. Simple calculation enables students to work out the correct answer quickly and accurately in a short time.

2. Simple operation is different from elementary arithmetic. It does not operate according to the operation order of elementary arithmetic, but uses various operation properties and laws, which is a special operation mode.

3. There are many kinds of "simple operation" test questions, which can be generally divided into two categories: operation with "operation law" and operation with "operation nature".

4. Using simple calculation methods in mathematics can greatly save the time of doing problems.