Dislocation addition and subtraction

The numerator and denominator are enlarged or reduced by the same multiple at the same time, and the value of the fraction remains unchanged.

When the form and order of the options in the topic are the same, only the significant figures of the results need to be considered, and the calculation results generally do not need decimal points.

Effective number method

From the first non-zero digit on the left to the last non-zero digit is called a valid digit.

In other words, deleting all zeros before the number is a valid number.

Mantissa method

Get the answer by asking the last person in the result.

1) Calculate to the last few digits according to the option;

2) The digits after the decimal point shall prevail, and the missing digits shall be supplemented by 0;

3) Add first and then subtract.

Characteristic number method

Turn the percentage into a close fraction, you can subtract it first and then calculate it, which simplifies the operation steps.