Question 10 There seems to be a misunderstanding upstairs. Set a is {1/2, 1/3, 1/4, 1/5? , 1/6? , 1/7}, not "possible", but the set b is {3,5,7}. Set multiplication should be the intersection of sets, which becomes the product of arbitrary elements here, so only 1 is the product. There seems to be no such definition in China's math book. To tell the truth, I don't understand this question either.

Question 13. II should be converted into 2+[ 1/(x-4)]. Obviously, g(x) is an inverse proportional function of X, and so is III. This kind of problem should be simplified to a simple form, and you can see it clearly by drawing a picture. There should be both positive and negative. You are right.

Finally, the question 1 1. This question is like a puzzle. I want to find a universal equation, so that you can do the same next time you encounter similar problems, but I can't. I drew a picture, and each point can be represented by coordinates. The starting point is (A 1, B 1) and the ending point is (A7, B6).

In this way, there are three possibilities from the starting point to (A3, B2) and three possibilities to symmetry (A2, B3). The possibility of reaching (A3, B3) is 3+3 = 6; There are four possibilities (A4, B2); The possibility of reaching (A4, B3) is 4+6 =10; There are also 10 possibilities to achieve symmetry (A3, B4). So it is an increasing sequence. The possibility of reaching point B (A4, B4) is that the sum of two possibilities (A3, B4) and (A4, B3) must pass through one of these two points, that is, 20 kinds. There are 10 possibilities from point B to the finish line. Multiply the two possibilities and it is 200.