2. Derivation of triangle area formula: put two identical triangles into a parallelogram.
3. Derivation of trapezoid area formula: Put two identical trapezoids into a parallelogram.
4. Derivation of circle area formula: Transform a circle into an approximate rectangle.
5. Derivation of the cylinder volume formula: transform the cylinder into a cuboid.
6. Take the whole ten or hundred in simple calculation, such as: 253-99=253- 100+ 1.
7. Transformation of numbers and formulas: 25× 16=25×4×4 16 is transformed into 4×4.
8. Number to number conversion:1÷ 0.125 =1÷1/8
..... ratio, division, fraction, decimal, percentage conversion, etc.