Second, the integer mixed operation, the operation order is easy to make mistakes.

Third, the application of multiplication formula is not skilled.

Understanding angle: the angle has nothing to do with the length of the sides, but with the size of the mouths on both sides.

5. Time, minutes, seconds, unit conversion is easy to make mistakes.

Six, measuring the length, the ruler is not standardized, the reading ruler is not accurate, and the unit conversion is easy to make mistakes.