The first question; According to the meaning of the question, the remaining two parties are 400 sets, and Party A sells four times as much as Party B, and it turns out that Party A is 8/7 times as much as Party B. ..

Suppose b has x units.

8/7x-400=(x-400)*4

X=420...b

420*8/7=560 ...

The second question will help you correct it. At the same time, two trains travel in opposite directions from A and B. They met for the first time in C, 40km away from A. After meeting, the two trains continued to move at the original speed. They return immediately after arriving at their respective stations, and meet at D, which is 20km away from C. How many kilometers is it between A and B?

When we first met, car A traveled 40 kilometers, and the two cars walked the whole journey. From the beginning to the second meeting, the two cars walked three times. Because the speed is the same, so from the first meeting to the second meeting, the AB car * * * has made two full trips, and it is still 20 kilometers away from point C.

In the first case, D is on the right of C (40 * 2+20)/2+40 = 90km.

In the second case, D is to the left of C (40 * 2-20)/2+40 = 70km.

Because you didn't say who is faster, there are two answers.

The third problem is 20%+35%+45%= 100%. This is water, just one cup, and I drank it all, so it's the same.

The solution of the fourth question is the same as that of the first question.