Can anyone explain engineering to me in detail! Be detailed

I think so:

It takes 4 days for teams A and C to cooperate, so one day is 1 4. The work efficiency of B C is 7 9 of A and C, then the work efficiency of B C is.

1/4*7/9=7/36。The sum of the work efficiency of A and B is 10 7 of B and C, that is, 7 36 * 10 7 = 5 18.

A-C + B-C + A-B = 2 A + 2 B + 2 C, then divide by 2 = A + B + C so (1 4 + 7 36 + 5 18) 2

13 36 (A, B, C, cooperate for one day).

1) How many days does it take for A, B and C to complete it alone:

1 divided by 13 36 = 36 13 = 2 and 10 13 (days) (2) A first repairs 2 days, and then B and C repair 3 days, how many days does it take for the rest of the cooperation to be completed?

A = A, B, C-B, C, = 13, 36-7, 36=6, 36=1, 2, 6.

1-1 6*2-7 36*3) divided by 13 36 = 1 12 divided by 13 36

3 13 (days).

Answer: (1) It takes 2 and 10 13 days for A, B and C to complete it separately. (2) A will repair for 2 days, and then B and C will repair for 3 days, and the rest of the cooperation will take 3 13 days to complete.

Got it? If you don't understand, just ask. Study hard and use your brain.

Solution: The total engineering quantity of building a highway is 1, the work efficiency of A is x, the work efficiency of B is y, and the work efficiency of C is z, then: A needs 1 x days to complete alone, B needs 1 y days to complete alone, and B needs 1 z to complete alone

1/（x+z）=4

y+z=7/9(x+z)

x+y=10/7(y+z)

It is available from above. x=1 6 A needs 1 x = 6 days to complete alone, y=1 9 B needs 1 y = 9 days to complete alone, z=1 12 B needs 1 z = 12 days to complete alone, and the rest of the cooperation needs [1-2x-3(y+z)] (x+y+z)=3 13 days.

It's a 3 yuan 1st order equation, brother, assuming that the efficiency of the three teams is x, y, z, and the engineering quantity is set to 1, then the three teams need 1 x days, 1 y days, and 1 z days to complete each.

Here's the equation:

1/(x+y)=4

y+z=(x+z)*7/9

x+y=(y+z)*10/7

Solve it yourself.

Let A, B, and C need x, y, and z days respectively, then the system of equations 1 x+1 z=1 4;1 /y+1/z=1/4×7/9=7/36；1/x+1/y=10/7×7/36=5/18。The solution gives x=6, y=9, z=12

1-1/3-7/36x3=1/12

The second question is unclear.

You're a student, ask such a question, and many of the types of application problems in math textbooks in elementary school are based on your model.

A efficiency 1 20, B efficiency 1 30

Cooperation takes 1 (1 20 + 1 30) = 12 hours.

A has more completions than B: 12 20-12 30 = 1 5 Total number of parts: 96 1 5 = 480.

A efficiency 1 10, B efficiency 1 12, C efficiency 1 15 C gang A: (1-8 10) 1 15 = 3 hours.

C B: (1-8 12) 1 15 = 5 hours.

There are a total of 480 Lingjian parts.

Method: Total x

x (x 20 + x 30))*x 20-x 30)=96

Let A and B cooperate for x days, x 30 + (40-x) 50 = 1, and the solution x is 15 days