Let the existing water quantity be a, the water quantity gushed out per minute be b, and the water quantity pumped out by the pump per minute be c, and list the equations according to the meaning of the topic:
2C×40=A+40B
4C× 16=A+ 16B
Solution: a = 80b, c = 3/2b.
If you want to finish pumping water in 10 minutes, you need at least x pumps, including:
CX× 10=A+ 10B
Substituting a = 80b and c = 3/2b into the above formula, we get:
15BX=90B
X=6
Answer: 10 minutes requires at least 6 pumps to finish pumping water.
2. Several students have to pay 2.85 yuan for photos (there are two photos), and 0.48 yuan for developing another photo. The average amount of money booked does not exceed 1 yuan, and all of them are assigned a photo. How many students are there at least?
If two people take a group photo, each person has to pay 2.85/2 = 1 .425 yuan more than1yuan, which is not in line with the meaning of the question.
There is a photo of X people (x>2).
Everyone is assigned a photo, so the total number of photos is X.
Because there are two photos in the photo shoot, x-2 photos need to be developed.
So the cost is 2.85+0.48(x-2)
The average money paid by each person is [2.85+0.48 (x-2)]/X.
According to the meaning of the question, the average payment per person does not exceed 1 yuan.
Then [2.85+0.48(x-2)]/x≤ 1
The solution is x≥3.6.
X is a positive integer because it is the number of people.
So x takes 4 as the minimum value.
So at least four students took part in the photo shoot.
3. Someone 10: 10 left home to catch the train at 1 1 0, and his home is 10 km from the station. He left home for 5 minutes at a speed of 3 km 1 hour, then took the bus to the station and asked how many kilometers the bus could walk at least every hour.
Let the speed be x.
( 10-3 * 5/60)/x & lt； =(50-5)/60
10- 1/4 & lt； = 1 1/ 12x
x & gt= 10.64
That is, the speed is at least10.64 km/h.