0.78×98

=0.78×( 100-2)

=0.78× 100-0.78×2

=78- 1.56

=76.44

Problem solving analysis: multiplication of two numbers. Because 98 is a two-digit integer close to 100, we consider using 100 to represent this number, so we need to multiply the two numbers with the multiplicand 0.78, so in the first step, we use 100 and 2 to represent 98, and in the second step, we use the multiplication and distribution law to make the multiplicand 0.78 and 100 respectively.

In the current textbooks, only "multiplication" is said, not "multiplication". Pay attention to the difference between "division" and "division" in Division. Dividend precedes division, and divisor precedes divisor.

Simple operation makes use of the basic properties of arithmetic and numbers, which makes the calculation simple and makes it easy to calculate numbers from a very complicated formula.

The most commonly used method in simple calculation is multiplication and distribution law. Ax(b+c)=axb+axc where a, b and c are arbitrary real numbers. On the contrary, axb+axc=ax(b+c) is called the inverse application of multiplication and division (also called finding common divisor), especially when A and B are complementary to each other, this method is more useful.

References:

Baidu Encyclopedia Entry-Simple Calculation