A 0 0

a a 1

0 a a/ 1

Do it:

69.09 (Pay attention to the alignment of decimal points)

38.92 (careful calculation should be paid attention to)

0.208 (pay attention to the position of decimal point)

100 (pay attention to carry)

10/3 (attention should be paid to simplification)

20/ 1 (calculation should be paid attention to)

Additive associative law:15+28+12 =15+(28+12) (12 was written by myself) a+b+c=a+(b+c).

Multiplicative commutative law: 15×28=28× 15 ab=ba.

Multiplicative associative law:15× 28×12 =15 (28×12) ABC = a (BC)

Multiplication and distribution law: (28+ or-15 )×12 = 28×12+or-15× 12 (a+ or -b)×c=ac+.

1.

=(7/2+7/5)×4

= 1×4

=4

Using the laws of multiplication and distribution.

Do it:

Original formula =8.5- 10.4÷ 1.3.

=8.5-8

=0.5

Original formula = (5× 5/2 )× (3/1×10/3)

=2+ 10/ 1

=2 and 10/ 1

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2.

Equivalence relation: number of six classes (1)+ number of six classes (1) ×4/ 1= number of six classes (2).

32+32×4/ 1

=32+8

=40 (pieces)

A: Class 6 (2) handed in 40 works.

Do it:

( 16.5- 15)÷ 15

= 1.5÷ 15

=0. 1

= 10%