Using the method of extracting common factor, the formula: ac+ab=a(b+c), extracting common factor 2.5, 1.2, 0.8, adding them together just makes the operation simple.

1.2×2.5+0.8×2.5

=( 1.2+0.8)×2.5

=2×2.5

=5?

2、46×44/45

In this problem, firstly, 46 is converted into (45+ 1) by the law of additive distribution, and then the operation is simple by the law of multiplicative association: (a×b)×c=a×(b×c).

46×44/45

=(45+ 1)×44/45

=45×44/45+44/45

=44+44/45

=44 and 44/45

3、 1.6×7.5× 1.25

In this problem, 1.6 is converted into 2×0.8 by the law of multiplicative distribution, and then rounded up by the law of multiplicative association: (a×b)×c=a×(b×c) for simple calculation.

1.6×7.5× 1.25

=2×0.8×7.5× 1.25

=(2×7.5)×(0.8× 1.25)

= 15× 1

= 15

4、250+6 16÷28× 15

In this problem, firstly, 6 16 is converted into 560+56 by the distribution method, then the common divisor 28 is extracted, and then a simple operation is performed according to the multiplicative associative law.

250+6 16÷28× 15

=250+(560+56)÷28× 15

=250+(20+2)× 15

=250+300+30

=580

5、35x62+70x 19

In this problem, firstly, 70 is converted into 35 and 2 by using the multiplicative distribution law, then the common divisor 35 is extracted by using the inverse application of the multiplicative distribution law, and finally a simple calculation is made by using the multiplicative associative law.

35x62+70x 19

=35x62+35x2x 19

=35x62+35x38？

=35×(62+38)

= 100×35

=3500