A piece of work, A and B together take 4 hours to complete

Solution: From the meaning of the question, 1 4 represents the workload of A and B for 1 hour, and 1 5 represents the workload of B and C for 1 hour.

1 4+1 5) 2 9 10 indicates the amount of work that A has done for 2 hours, B has done 4 hours, and C has done 2 hours.

According to "After A and C do 2 hours together, the remaining B needs to do 6 hours to complete", it can be seen that A does 2 hours, B does 6 hours, and C does 2 hours, and the total workload is 1.

So 1 9 10 1 10 means that B does 6-4 2 hours of work.

1 10 2 1 20 indicates B's work efficiency.

1 1 20 20 hours means that it takes 20 hours for B to complete alone.

A: It takes 20 hours for B to complete alone.

After 2 hours of A and C, B does 6 hours, it can be divided into 2 hours for A and B, 2 hours for B and 2 hours, and B for 2 hours.

A and B do 2 hours, B and C can be completed in 2 hours: 1 4 2 + 1 5 2 9 10 B can be done in 2 hours: 1-9 10 1 10

B does this work alone: 2 1 10 20 hours.

20 hours.

4(a+b）=1

5(b+c)=1

2(a+c)+6b=1

The solution yields b = 1 20

It takes 20 hours for B to complete this work alone.

Regard this total engineering quantity as 1, so the efficiency of A and B cooperation is 1 6, and the efficiency of A alone is 1 10, so B needs to do it alone.

15 So it takes 15 hours for A to do alone.

A: B = 2:1

A = 1/6

B = 4 - (1/6 times 4) = 1/3

1/3 divided by 4 = 1/12

1) 1 1/12

A: It can be completed in 12 hours.

2) 1 - (1/6 times 1) = 5 of 6 regrets

2/3 - 1/6 = 2 points 1 of the Great Front Annihilation

1/2 (1/6 + 1/3) = 1

A: It will take 1 hour.

For a job, it takes 4 hours for A and B to work together, and it takes 6 hours for A to do it alone.

1) How many hours does it take for B to do it alone?

B completes the work every hour.

1/4 6/6 1/12 coarse

B alone does the completion required.

1 1/12 12 hours.

2) After A does 1 hour and B joins the cooperation, how many hours will it take to complete two-thirds of the work?

A completes the work in 1 hour.

1/6 1 1/6

A and B cooperated to complete the work.

2/3 1/6 1/2 1/2

The cooperation completion time is.

1/2 1/4 2 hours.

Let B alone take x hours, then (1 12 + 1 x)*4 + 6 x =1 solution x=15 1 ( 1 12 + 1 15)= 20 3 so it takes 20 3 hours.

B alone: 1 [(1-4 12) (4+6)] = 15 days.

A and B should be used together: 1 (1 15 + 1 12) = 20 3 hours.

A does 1 per hour of radical attack on Youzen La, and B does 1 5 per hour

Hours = Hours.

Hello: This is an engineering problem, look at the workload as unit 1Therefore, A completes all 1 3 in 1 hour, and B completes 1 4

1 and 5 7 (hours).

1 3 = one-third (hour) 1 4 = one-quarter (hour) This is the efficiency of the two of them.

One-third quarter = seven-twelve

1 7/12 = 12/7 (hours).

Answer: It takes 12/7 of the time for cooperation between A and B.

Solution: A ergonomics: 1 3

B Efficacy: 1 4

After half an hour of cooperation between A and B, the remaining part will be completed by B alone, and the following needs to be required

2 and 5 6 hours.

Let this work be 1, then 1 (1 3 + 1 4) equals 12 7 hours. That is, the total amount of work divided by the efficiency of A and B and equal to the working hours.

Think of the total amount of work as the unit "1", so.

A completes one-third of the total.

B completes a quarter of the total.

1 3 + 1 4 = 7 12, just turn 12/7 upside down (count) down.

30 * A tung rot = 24 * (A + B) A = 4 B.

Total workload = 30 * Leakage of the first office.

30 * A-10 * A-5 B (remainder) * A + B) 15 hours.