The fifth grade of primary school equation, etc Somebody got 240 yuan There are three kinds of RMB, 2 yuan, 5 yuan and 10 yuan, a total of 50 pieces Among them, the number of 2 yuan and 5 yuan are the same How many pieces are there for 10 yuan? Express it in equation. Thank you. I'm teaching my niece. It doesn't matter if I'm old

Let 2 yuan quantity = 5 yuan quantity = x pieces, 10 yuan quantity = 50-2x pieces
(2+5)X+10(50-2X)=240
The solution is x = 20
50－2X=10
20 for 2 yuan, 20 for 5 yuan, and 10 for 10 yuan

1. When measuring the depth of the well at the wellhead, when the rope is folded in half and dropped to the bottom of the well, there is still 8 meters left; when the rope is folded three times (I don't know whether it is folded into three parts or folded three times), there is still 2 meters left when it is dropped to the bottom of the well. How many meters are the depth of the well and the length of the rope?
2. The father said to his son, "when I was your age, you were only 4 years old; when you were my age, I was 79 years old." How old are father and son now?

If the well depth is x meters, the rope length is 2 (x + 8) meters
2（x+8）=3（x+2）
x=10
Rope length 2 * (10 + 8) = 36m
The analysis with topic meaning is folded into three parts
2,（79-4）%3=25
4 + 25 = 29 years old
79-25 = 54 years old
A: my father is 54 and my son is 29

The railway from Changsha to Guangzhou is 726 kilometers long. A freight train runs 69 kilometers per hour from Changsha to Guangzhou. One hour after the freight train leaves, a passenger train runs 77 kilometers per hour from Guangzhou to Changsha. In a few hours, the two trains will meet? (made before 2:00 this afternoon.)

Let the two cars meet in X hours
69*(X+1)+77X=726
69X+69+77X=726
146X=657
X=4.5
The two cars will meet in 4.5 hours

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