I still don t understand the problem of cows eating grass, so please let me know

Cow grazing problem concept and formula.

The problem of cattle grazing, also known as the problem of growth and decline or Newton's pasture, was proposed by the great British scientist Newton in the 17th century. The condition of a typical cow grazing problem is to find how many cows can eat the same grass by assuming that the growth rate of grass is fixed, and the number of days it takes for different numbers of cattle to eat the same grass is different. Because the number of days eaten is different, and the grass grows every day, the stock of grass constantly changes with the number of days the cow eats.

There are four basic formulas commonly used to solve the problem of cattle grazing, which are:

Set the amount of grass a cow eats in a day to "1".

1) the growth rate of the grass (the corresponding number of cows, the number of days eaten more, the corresponding number of cows, the number of days eaten less) (the number of days eaten more, the number of days eaten less);

2) The amount of original grass, the number of cattle heads, the number of days eaten, the growth rate of grass, the number of days eaten; `

3) the number of days eaten, the amount of original grass (the number of cows, the growth rate of grass);

4) The number of cattle heads, the amount of grass, the number of days eaten, and the growth rate of grass.

These four formulas are the basis for solving the problem of growth and decline.

Since the grass is constantly growing in the process of grazing in the process of cattle grazing, the key to solving the problem of growth and decline is to find ways to find invariants from change. The original grass on the pasture is unchanged, and although the new grass is changing, the amount of new grass growing every day should be the same because it grows at a uniform rate. It is because of this invariant that the above four basic formulas can be derived.

The problem of cattle grazing is often given that different numbers of cattle eat the same grass, and the field has both the original grass and the new grass that grows every day. Due to the different number of cows that eat grass, find out how many days the grass in the field can be eaten by several cows.

The key to solving the problem is to figure out the known conditions, conduct comparative analysis, and then find the number of new grass growing every day, and then find the amount of original grass in the grassland, and then solve the problem that the question is always asked.

The basic quantitative relationship for this type of problem is:

1.(Number of cows, days of grazing more - number of cows, number of days of grazing) (number of days of eating more - days of eating less) = the amount of new grass growing in the grass per day.

2.Number of cows Grass days - new growth per day Number of grass days = original grass in the meadow.

How to solve multiple meadows.

For the problem of "cattle eating grass" in multiple grasslands, in general, find the least common multiple of multiple grasslands, which can reduce the difficulty of calculation, but if the data is large, it is relatively simple to unify the area as "1".

It's been growing all the time when I eat it.

Set each entrance to enter x people per minute, the number of spectators per minute is z, and the number of people queuing before 9 o'clock is y

3×9x=y+9z

5×5x=y+5z

Eliminate x, y = 45z

y/z =45

So the first spectator arrived at 8:15

3*9=27

A: The first audience arrives at 8:15

1) the growth rate of the grass (the corresponding number of cows, the number of days eaten more, the corresponding number of cows, the number of days eaten less) (the number of days eaten more, the number of days eaten less);

2) The amount of original grass, the number of cattle heads, the number of days eaten, the growth rate of grass, the number of days eaten; 3) the number of days eaten, the amount of original grass (the number of cows, the growth rate of grass);

4) The number of cattle heads, the amount of grass, the number of days eaten, and the growth rate of grass.

Suppose the grass that a cow eats in a day is the unit "1".

Then the grass that grows every day is [21*8-24*6] [8-6]=12 units, and it turns out that there is grass is 24*6-6*12=72 units.

To never finish eating, that is, the amount of grass eaten every day is equal to the amount of growth, that is, to:

12 1 = 12 cows.

Equation solution: Let the pasture have a grass amount x, the grass grows y every day, and each cow eats a certain amount of grass per day (x+6y) (24*6)=(x+8y) (21*8)(x+6y) 6=(x+8y) 7

x=6y, set a maximum of m cattle pasture, and never finish the pasture.

x+6y)/(24*6)=y/m

12y/(24*6)=y/m

m=12 (only).

If 13 cows eat for five days, this is not an even possible situation: 3 cows eat for 20 days and 12 cows eat for 5 days, which is satisfied without counting the grass growth (the grass growth is 0).

What's more, if there are 13 cows, one more cow will definitely not be enough to eat (unless the grass is negative), and the denominator of the formula you give is 20-4 days wrong.

First of all, your question itself is unreasonable, 13 cows eat for 5 days, assuming that the cows eat grass at a rate of 1, then the cows eat (13 5 1) units of grass, that is, 65 units of grass. Then 3 cows ate 60 units of grass for 20 days, but on the 5th day there were 65 units of grass, why did they only have 60 units of grass on the 20th day? Unless the grass is ruined, so it grows negatively.

And you wrote the title incorrectly, it was eaten by 4 cows, and it was eaten in 13 days. Not 13 cows to eat, 4 days to eat)