Anthony, Brian and Chris are hired for a job. If Anthony and Brian are working together they will finish the job in minutes. If Anthony and Chris are working together they will finish the job in minutes. If Brian and Chris are working together, they will finish the job in hour. If the Chris is working alone, how long will it take him to finish the job

12.5

Step-by-step explanation:

Let  individual time taken by Anthony, Brian and Chris = t1 , t2 , t3 respectively

So, total time taken by A & B  = 1 / t1  + 1 / t2 , lets suppose = 10  {i}

Total time taken by A & C = 1 / t1  + 1 / t3 , lets suppose = 15 {ii}

Total time taken by B & C = 1 / t2  + 1 / t3 , lets suppose = 20 {iii}

From {i} , 1 / t2 = 10 - 1 / t1

From {ii} 1 / t1 = 15 - 1 / t3

By above two eqtns ,  1 / t2 = 10 - (15 - 1 / t3)

1 / t2 = 1 / t3 - 5

Putting in {iii} , 1 / t3 - 5 + 1 / t3 = 20

2 / t3 = 25

t3 = 12.5