it takes two computers 15 minutes to the job. If it takes ca 45 minutes to do the job on its own, how long will it take cb to do the job on its own

Question

It is from Aleks

Answer 1

Together it takes 15 minutes so together

a and b do 1/15 of the job per minute.

1/a + 1/b = 1/15

 

a takes 45 minutes alone so a does 1/45

of the job per minute.

 

1/45 + 1/b = 1/15

1/b = 1/15 - 1/45

1/b = 3/45 - 1/45

1/b = 2/45 = 1/22.5

 

Computer b alone would take 22.5 minutes.