Answer:
Sam can do the job in 20 min. So he can do the whole job at the rate of 1 job in 20 minutes.
So he does 1/20 of the job per minute.
.
Rob can do the job in 30 min. His rate is 1/30 of the job per minute.
.
Working together how does it take?
.
1/20*x + 1/30*x = 1 job done
, where x = minutes.
.
Step-by-step explanation:
