There are three main methods: addition and subtraction rounding, grouping rounding and raising common factor.
They all use the idea of splitting and rounding in mathematical calculation.
Main steps:
① When encountering a complex formula, first observe whether it is possible to round up;
(2) Make a whole 100 by four operations, and then make a simple calculation.
Addition-subtraction rounding method
1, split a certain number in the calculation formula to make it and other numbers make up a whole ten, and the whole hundred is1;
2. Add a number, which can be rounded by other numbers, and finally subtract this number.
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Group rounding method
In the calculation problem with only addition and subtraction, the items in the calculation formula are recombined and rounded, and two formulas are mainly adopted: Teacher G talks about the Olympic number (micro). Example 3
Additive associative law: a+b+c = a+(b+c) = (a+b)+c;
The essence of subtraction: a-b-c=a-(b+c).
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Methods of improving common factor
Find the common factor by multiplication and division, a x (b c) = a x b a x c;
If there is no common factor, the common factor can be changed according to the multiplicative associative law, as shown in Example 4.
a×b=(a× 10)×(b÷ 10)，
a×b \c = a \c×b，
a×b×c=a×(b×c).
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