There is a bicycle whose front and rear wheels are the same size. The front wheel can ride 5000 km from the beginning of use to the end of life, and the rear wheel can ride 3000 km from the beginning of use to the end of life. In order to make the two tires scrapped together, Xiao Ming removed the rear wheel and used it as the front wheel after riding for a period of time

There is a bicycle whose front and rear wheels are the same size. The front wheel can ride 5000 km from the beginning of use to the end of life, and the rear wheel can ride 3000 km from the beginning of use to the end of life. In order to make the two tires scrapped together, Xiao Ming removed the rear wheel and used it as the front wheel after riding for a period of time

1875km

Original title:
Congcong: "my hometown has two elder sisters who went to the market to sell jujubes. They brought a total of 50kg jujubes. On the way back to the village, they talked about the market. It turned out that one of them brought more jujubes, and the other one brought less jujubes, but they sold the same amount of money. The second elder sister said," if I have so many jujubes, I can sell them for 162 yuan. "The elder sister said," if I have so many jujubes, I can sell them for 72 yuan. "
Mingming: "who brings more dates?"
Congcong: "ha ha! You need to judge this by yourself. There is no hint. My question is: how many kilos of jujube each of the two sisters brought? How much do they each sell for each kilogram of jujube?"
Mingming: "I already know the answer, students, have you worked it out?"

Suppose the eldest sister has x kg jujube, then the second sister has (50-x) kg jujube. [162 / (50-x)] * x = [72 / x] * (50-x) 162x ^ 2 = 72 (50-x) ^ 2 [(50-x) / x] ^ 2 = 162 / 72 = 9 / 4 (50-x) / x = 3 / 2x = 20. The eldest sister sells 72 / 20 yuan / kg jujube, and the second sister sells 162 / (50-20) = 5.4 yuan / kg

How to do the third question on page 15 of the winter vacation homework of primary school in 2011?
It's the Jiangsu Education Press. The title is: a building with 25 floors above the ground and three floors below. If the number above the ground is positive, the height of the building is 3 meters.
1. Take the elevator from + 1 floor to + 18 floor, up? rice
2. From the 6th floor to the 1st floor, does the elevator go down? rice
3. Take the elevator up 27 meters from the - 2 floor to the other floor. What's the record of this floor?
Please make a formula

1. How many floors have you risen? If you look at the foot, it's 18-1 = 17 floors, 17 * 3 = 51 meters
I think I haven't learned negative numbers in primary school, so I divide it into two parts
From the sixth floor to the first floor, it dropped five floors
From the first floor to the negative floor, it has dropped by 1 floor (Note: there is no 0 floor.), so it has dropped by 5 + 1 = 6 floors in total
The sixth floor is 6 * 3 = 18 meters. So it's 18 meters down
3. From the negative second floor to the first floor, it rose by two floors. The two floors are 2 * 3 = 6 meters. So the ground rose by 27-6 = 21 meters. It's 21 / 3 = 7 floors
1 + 7 = 8, so he's on the eighth floor, and it's + 8
I don't know if the floor here means "building". We didn't learn this version

The winter vacation homework of grade 5 of primary school in 2011

=(0.7+0.3)x7.6
=1x7.6
=7.6