1. Make a simple calculation by using the additive combination law.

(A+B)+C = A+(B+C) or a+b+c+d=(a+c)+(b+d)

For example 1, 5.76+ 13.67+4.24+6.33.

=(5.76+4.24)+( 13.67+6.33)

= 10+ 10

=20

Example 2, 37.24+23.79- 17.24

=37.24- 17.24+23.79

=20+23.79

=43.79

Second, use the law of multiplicative association to make simple calculations: this kind of problems often include multiplication between special numbers.

(a×b)×c=a×(b×c)

Multiplication between special numbers:

25×4= 100 125×8= 1000 25×8=200 125×4=500

Example 3,4× 3.78× 0.25

=4×0.25×3.78

= 1×3.78

=3.78

Example 4: 125×246×0.8

= 125×0.8×246

= 100×246

=24600

2.5×0. 125×8×4, etc. If division is also applicable, or division is converted into multiplication to calculate, such as 8.3×67÷8.3÷6.7, etc.

Thirdly, the multiplication and distribution law is used for simple calculation:

(a+b)×c=a×c+ b×c

(a-b)×c=a×c- b×c

Do this kind of problem, don't rush to calculate. First of all, you must analyze the special relationship between numbers. Just be sure to observe carefully and find the trick to do the problem.

Example 5, (2.5+ 12.5) × 40

=2.5×40+ 12.5×40

= 100+500

=600

Example 6, 3.68× 4.79+6.32× 4.79

=(3.68+6.32)×4.79

= 10×4.79

=47.9

Example 7.26.86× 25.66-16.86× 25.66

=(26.86- 16.86) ×25.66

= 10×25.66

=256.6

Example 8, 5.7× 99+5.7

= 5.7×(99+ 1)

=5.7× 100

=570

Multiplicative distribution law is used for simple calculation. When you divide by a number, it is first multiplied by the reciprocal of a number and then distributed.