Answer: 28/3 hours
Explanation:
From the question, Kim and Josh can clean a house together in 3 hours while Kim alone uses 7 hours to clean the house by herself.
Kim's hourly rate will be to clean the house = 1/7 per hour.
In 4 hours:
Kim will have completed = 1/7 × 4 = 4/7 of the house
This mean that Josh completes:
1 - 4/7 = 3/7 of the house.
Josh's hourly rate will now be:
1/4 × 3/7 = 3/28 of the house per hour.
From Josh to clean the house alone, he will use:
= 1 ÷ (3/28)
= 1 × 28/3
= 28/3 hours
Josh will use 28/3 hours to clean the house alone?