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Ask three practical questions 1. A pool is equipped with an inlet pipe and an outlet pipe. If the inlet pipe is opened only, the empty pool can be filled in 8 minutes. If the outlet pipe is opened only, the full pool can be drained in 12 minutes. Now, if the inlet pipe is opened only 2 minutes later, how many minutes will it take to fill the pool? 2. For a pool, it takes 10 hours to open a water inlet pipe to fill it, 12 hours to open B water inlet pipe to fill it, and 30 hours to open C water outlet pipe to fill a pool. How many hours to open three pipes at the same time to fill the empty pool? 3. A pool can hold 84 tons of water. There are two water injection pipes to fill the pool. The first pipe can fill the pool in 8 hours, and the second pipe can fill the pool in 6 hours. Now the two pipes are opened at the same time. When the pool is filled, how many tons of water can the second pipe fill the pool?
These three problems are primary school mathematics engineering problems, know the time, you can use a fraction of work efficiency, unit 1 is the total amount of work
1. A pool is equipped with an inlet pipe and an outlet pipe. If the inlet pipe is opened only, the empty pool can be filled in 8 minutes. If the outlet pipe is opened only, the full pool can be drained in 12 minutes. Now, if the inlet pipe is opened only 2 minutes later, how many minutes will it take to fill the pool?
（1-2/8）/（1/8-1/12）=18
2. For a pool, it takes 10 hours to open a water inlet pipe to fill it, 12 hours to open B water inlet pipe to fill it, and 30 hours to open C water outlet pipe to fill a pool. How many hours to open three pipes at the same time to fill the empty pool?
1/（1/10+1/12-1/30）=20/3
3. A pool can hold 84 tons of water. There are two water injection pipes to fill the pool. The first pipe can fill the pool in 8 hours, and the second pipe can fill the pool in 6 hours. Now the two pipes are opened at the same time. When the pool is filled, how many tons of water can the second pipe fill the pool?
1/（1/8+1/6）=24/7
（84/6）*（24/7）=48
Ask three practical questions
1. There are 56 students in class 3 of grade 5, which are arranged in two columns with 28 students in each column. If the order is the same, please ask three students in each adjacent column to come out each time. How many different ways are there in total?
2. Mr. Zhang bought a piece of rectangular paper 120 cm long and 45 cm wide, and cut it into square paper of the same size without surplus. How long can the side length of the square paper be?
1. (28-2) Chinese version
The greatest common divisor of 2.120 and 45 is 15
So the longest side length of square paper can be 15 cm
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