Question

Mary can do a job in 80 minutes, Working with Jané, both can do the job in 30

minutes. How long will it take Jane to do the job alone?

Answer 1

see below

Explanation:

The equation to determine the work time is

1/a+1/b = 1/c where a and b are the times alone and c is the time together

1/80 + 1/30 = 1/c

Multiply by the least common denominator to clear the fractions, which is 240c

240c(1/80 + 1/30 = 1/c)

3c+8c = 240

11c = 240

Divide by 11

11c/11 =240/11

c = 240/11 minutes

c=21.81818

Approximately 22 minutes