Question

Machines A,B and C can complete a certain job in 30 min., 40 min. and 1 hour respectively. How long will the job take if the machines work together?

Answer 1

time taken by the machine A,B and C together =

A work in 1min = 1/30

B work in 1min = 1/40

C work in 1min = 1/60

A+B+C=

1/30 + 1/40 + 1/60 = 9/120

In 1min they do 9/120 work

Total time taken to do this work =120/9min=13.33min