Unit 1 four arithmetic operations

1, operation sequence

P5: In the formula without brackets, if there is only addition and subtraction or only multiplication and division, it must be calculated.

For example: 98-46+25 6÷3×98

= =

= =

P6: In the formula without brackets, there are multiplication, division, addition and subtraction, which must be calculated first.

For example: 36+64÷4

=

=

P 1 1: If there are brackets in the formula, it must be calculated first.

For example: 100(4+2 1)

=

=

2.P 12:, and are collectively called four operations.

3.P 13: Operation on 0

Add a number to 0 and you get the number.

Subtract 0 from a number and you get the number.

Multiply a number by 0 to get 0.

Divide 0 by a number to get 0.

0 cannot be divided completely, for example, 5÷0 does not exist and is meaningless.

4. Elementary arithmetic methods.

Look (numbers, operation symbols, thinking about the operation order. )

Draw a line (draw a line, which step is counted first, draw a horizontal line under which step, and copy if it is not counted. )

Three calculations (calculated in order of operation)

Check (check whether the operation sequence is wrong and the calculation is wrong. )

Unit 3 Algorithm and Simple Calculation

1, algorithm and formula characteristics

Characteristics of Examples of Arithmetic Formula

P28:: additive commutative law a+b=b+a 34+89+66=34+66+89.

26+47-6=26-6+47 1, only addition and subtraction.

2. Pay attention to exchange the previous "-"signs when subtracting.

3. In simple calculation, additive commutative law and additive associative law are generally used at the same time.

P29: additive associative law

a+b+c=a+(b+c)

88+ 104+96=88+( 104+96)

79+26-9=26+(79-9)

P34: Multiplicative commutative law a × b=b× a 4×58×25=4×25×58 1, only multiplication.

2. Multiplicative commutative law and multiplicative associative law are generally used at the same time in simple calculation.

3. Pay attention to finding good friends:

2×5= 10

4×25= 100

8× 125= 1000

P35: Multiplicative associative law

a×b×c

=a×(b×c)

125×67×8=67×( 125×8)

P36: division by multiplication and division: (a+b)×c

=a×c+b×c

Combination: a×b+a×c

=a×(b+c) 25×(200+4)=25×200+25×4

265×105-265× 5 = 265× (105-5)1,with multiplication and addition; Or multiplication and subtraction.

2. When disassembling, divide the number outside the bracket into two numbers inside the bracket.

3. When merging, extract the same factor and add or subtract different factors.

Pay special attention to: the difference between multiplicative associative law and multiplicative distributive law.