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Honghong bought three pens and five notebooks, a total of 38.5 yuan. The price of a pen is twice that of a book. How many yuan does a pen cost! Two unknowns are the same
Pen price x, book price y
3x+5y=38.5
x=2y
y=3.5
x=7
7 yuan for a pen and 3.5 yuan for a book
Sixth grade math problem is best not to use equations to solve, you prawns help
For a project, it takes 20 days for team a to do it alone, and 15 days for team B to do it alone. After several days for team a to do it alone, team B will continue to do it and complete the task in 18 days. How many days did team a and team B do it respectively?
1/20x18=9/10
1-9/10=1/10
Party B: 1 / 10 (1 / 15-1 / 20) = 6 (days)
A: 18-6 = 12 (days)
To solve it, we need to solve the equation
1. The world-famous Great Wall, with a total length of 5000 kilometers, is built in the Qin, Han and Ming Dynasties. The length of the main body of the Great Wall built in these three dynasties is about 1:2:1.27. What is the main body of the Great Wall built in these three dynasties?
2. A 200m long train with a speed of 20m / s, how many seconds does it take to completely pass a 400m long bridge?
3. On a section of double track, two trains pass each other. Train a runs at a speed of 20 m / s, with a total length of 180 m, while train B runs at a speed of 20 m / s, with a total length of 160 M?
Linear equation of one variable
1. If x is set in Qin Dynasty, 2x is set in Han Dynasty and 1.27x is set in Ming Dynasty
X+2X+1.27X＝5000
Self interpretation
2. Set to x seconds
20X＝200+400
Self interpretation
3. It takes x seconds to drive in opposite directions
（20+20）X＝180+160
Driving in the same direction, you can never make a mistake, because the speed of the two cars is the same, no matter how long it takes, the distance between the two workshops can not be changed
It takes 7.5 hours for a middle school to plant trees outside the school. It takes 5 hours for the eighth grade students to plant trees alone. Now let the seventh and eighth grade students plant trees together for one hour, and then let the eighth grade students complete the rest. How many hours do it take?
Suppose that it takes x hours to complete, from the meaning of the question, 17.5 + 15x = 1, the solution is: x = 413
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