Using simple calculation methods in mathematics can greatly save the time of doing problems.
Simple arithmetic
1, additive associative law?
The law of additive combination is (a+b)+c=a+(b+c).
For example, 8+1+9 = 8+(1+9) = 8+10 =18?
2. additive commutative law?
a+c=c+a .
Such as 8+5=5+8= 13.
3. Multiplicative associative law?
(axb)xc=ax(bxc).
For example 3x2.5x4 = 3x (2.5x4) = 3x10 = 30. ?
4. Multiplication and distribution law?
(a+b)xc=axc+bxc .