Answer:
1/7 + r = 1/3
Step-by-step explanation:
Rocco takes 7 hours to do the job.
In 1 hour, Rocco does 1/7 of the job.
Rocco's rate is 1/7 job per hour.
It takes Giulia x hours to do the job.
In 1 hour, Giulia does 1/x of the job.
Let r = 1/x. Giulia's rate is r part of the job per hour.
Together, Rocco and Giulia take 3 hours to do the job.
In 1 hour, Rocco and Giulia do 1/3 of the job.
Together, their rate is 1/3 of the job per hour.
1/7 + r = 1/3
