One: the subsidy law. For example: 136 minus 47, plus 47 to 50' 136 minus 50. It's easier to calculate, and 86 plus 3 is the answer. You can also subtract 40 first and then 7. ?

Two: conventional method. For example:14+6+25+15+9+1+31+5+4.

Mathematics (Mathematics or maths, from the Greek word "Má thē ma"; Often abbreviated as "mathematics"), it is a discipline that studies concepts such as quantity, structure, change, space and information, and belongs to a formal science from a certain point of view. Mathematicians and philosophers have a series of views on the exact scope and definition of mathematics.

In the development of human history and social life, mathematics also plays an irreplaceable role, and it is also an indispensable basic tool for studying and studying modern science and technology.

Source: Baidu Encyclopedia-Mathematics