99.99*0.2= 19.998。

99.99*0.3=29.997。

99.99*0.4=39.996。

By analogy, we can find that when the multiplier has two digits and the number of digits is 0, the highest digit of the multiplier is smaller than the tenth digit of the multiplier by 1, the sum of the highest and lowest digits of the multiplier is 9, and the rest digits remain unchanged. For example, if the tenth digit of the multiplier is 6, then the highest digit of the multiplier is 5 and the lowest digit is 4.

It can be concluded that: 99.99 * 0.9 = 89.5438+0.

Find the scope of application of the law:

Finding the method in primary school is very simple. Only addition, subtraction, multiplication and division will not have the troublesome solution of square, although sometimes addition, subtraction, multiplication and division will have square.

Middle school is a little more difficult. If you add power to the square, you may use arithmetic progression to find the law. But if you study hard, it's still very simple.

There is basically no problem in finding patterns in universities. There may be, but the chances are slim, so don't worry.