The problem of cattle grazing, also known as fluctuation problem or Newton pasture problem, was put forward by Newton, a great British scientist in the17th century. Experts pointed out that the condition of typical cattle grazing problem is that the growth rate of grass is fixed, and the number of days required for different cattle to eat the same grassland is different. How many cows can eat this grassland for how many days? Because the eating days are different, the grass grows every day, and the stock of grass changes with the eating days of cattle. Four basic formulas are usually used to solve the problem of cattle grazing, namely:

(1) Growth speed of grass = corresponding number of bulls × days of eating more-corresponding number of bulls × days of eating less ÷ (days of eating more-days of eating less);

(2) The amount of original grass = the number of ox heads × the number of eating days-the growth rate of grass × the number of eating days;

(3) the number of days to eat = the original amount of grass ÷ (the number of cattle-the growth rate of grass);

(4) The number of ox heads = the original amount of grass, the number of days to eat+the growth rate of grass.

The key to solve the problem is to find out the known conditions and make a comparative analysis, so as to find out the number of new grass growing every day, and then find out the original number of grass in the grassland, and then answer the questions raised by general questions.