29x40

=(30- 1)x40

=30x40- 1x40

= 1200-40

= 1 160

1, using the characteristics of numbers to "round up"

To understand an object, we must grasp its characteristics, it is different. Numbers also have their own characteristics in the mathematics kingdom. Today, we mean that these figures are close to the whole ten, the whole hundred and the whole thousand, such as 98, 1002 and so on. When calculating, as long as these numbers are regarded as whole ten, whole hundred and whole thousand, the calculation can be simplified.

2. Shift "rounding"

Everyone has played with Rubik's Cube and building blocks, and sometimes they can't meet our requirements, but they can do it by moving a small position, and sometimes the calculation is the same. Shifting "rounding" means moving the position of the number to round according to the characteristics of the formula.