The problem of linear equation with one variable on the first day of junior high school··· When a bicycle is moving at a fixed speed in front of it, there is a car to catch up with. If the speed is 30km / h, it will catch up in one hour; if the speed is 35km / h, it will catch up in 40 minutes to find the bicycle speed

The problem of linear equation with one variable on the first day of junior high school··· When a bicycle is moving at a fixed speed in front of it, there is a car to catch up with. If the speed is 30km / h, it will catch up in one hour; if the speed is 35km / h, it will catch up in 40 minutes to find the bicycle speed

Let the bicycle speed be x, then (30-x) * 60 = (35-x) * 40, x = 20

The application of the first degree equation of one variable!
(1) For a ship sailing between a and B, it takes 4 hours downstream and 1 hour more upstream than downstream. It is known that the speed of the ship in still water is 18 km / h, so the speed of water flow can be calculated
(2) The distance between Party A and Party B is 30km. They set out at the same time and walk in the same direction. Party A is behind and Party B is ahead. If Party A travels 35km per hour and Party B 20km per hour, how long can party a catch up with Party B?
(3) Each tin sheet can be made into 18 tin bodies and 45 tin bottoms. One tin body and two tin bottoms can be made into one tin. There are 180 tin sheets. How many tin bodies and tin bottoms can be used to make the whole tin?
(4) The purchase price of a commodity is 200 yuan, the price is 300 yuan, and the profit margin at discount is 5%. How much discount is the commodity sold?
(5) If you know a two digit number, the number on the tenth digit is two times larger than the number on the single digit, and the two digit number is four times larger than the sum of the ten digit and the single digit
Write down the steps! Thank you!
OK, it will add points!

1. Let the water velocity be X4 (18 + x) = 5 (18-x) x = 2km / H2. Let x hours catch up with 35x = 20x + 30x = 2 hours. 3. Make box bottom with X sheets of iron 45x / 2 = 18 (180-x) x = 80 (80 sheets of iron making box bottom) 180-80 = 100 (100 sheets of iron making box body) 4. Discount rate is x300x = 200 (1 + 0.05) x = 0.7 (sell at a discount of 7). 5

Application of linear equation with one variable
The front wheel of a bicycle is scrapped after 5000 meters, and the rear wheel can only travel 3000 meters. How can the front and rear wheels be exchanged to make the wheel travel farthest?

The front and rear wheels are interchanged after X meters
（5000-x)/5000*3000=(3000-x)/3000*5000
3(5000-x)/5=5(3000-x)/3
9(5000-x)=25(3000-x)
45000-9x=75000-25x
16x=30000
x=1875
A: after driving 1875 meters, the front and rear wheels are interchanged, and the wheels travel the longest distance
All in all: 1875 * 2 = 3750 meters

According to the market information, a shopping mall adjusts the price of two existing air conditioners of different models in the shopping mall. One air conditioner can make a profit of 10% (relative to the purchase price) after price adjustment, and the other air conditioner will lose 10% after price adjustment. The price of the two air conditioners after price adjustment is exactly the same, so the shopping mall will sell the two air conditioners after price adjustment ()
A. Neither profit nor loss B. 1% profit C. 2% loss D. 1% loss