Last week, my mother bought some boxes of milk with 36 yuan in the supermarket. Today, she came to this supermarket again and found that every box of milk she bought last time was sold to 0.3 yuan. So my mother spent 36 yuan to buy this kind of milk, and found that she bought four more boxes than before. What is the original price of this milk? A: If the original price is X yuan, the current price is (X-0.3) yuan.

36 divided by X=36 divided by (X-0.3)-4.

It is troublesome to solve this problem. Usually it can't be solved upstairs.

My method: the original price is X yuan, and the current price is (X-0.3) yuan.

36/X times 0.3=4 times (X-0.3)

10.8=4X squared-1.2x.

2.7=X(X-0.3)

X= 1.8

Both A and B have to walk from A to B. A takes 40 minutes, B takes 30 minutes and B takes 5 minutes. How many points does B take to catch up with A?

Answer: Let the speed ratio of A and B be 3: 4, and let the time of B be the equation of X..

3(5+X)=4X

X= 15

So 15 minutes to catch up.

A shopping mall first increased the original price of color TV by 30%, and then wrote "big reward, 20% discount" in the advertisement. As a result, each color TV set earned more than the original price 1 12 yuan. What should be the original price of each color TV?

Answer: The analysis of equivalence relation is: actual selling price-original selling price = 1 12 (yuan).

The original price of each color TV is X yuan.

Solution: x = 2800