SOLUTION: It took Tom 7 hours to repair a car. It took Johnny 8 hours to do the same repairs. How long would it have taken them if they did the job together?

Question 173571: It took Tom 7 hours to repair a car. It took Johnny 8 hours to do the same repairs. How long would it have taken them if they did the job together?
Found 2 solutions by solver91311, josmiceli:
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
Tom can do the job in 7 hours which means he can do of the job in one hour. Likewise, Johnny can do of the job in one hour.

Together they can do of the job in one hour.

So they can do the whole job together in hour.

56 divided by 15 = 3 with a remainder of 11. So 3 hours

11/15 times 60 minutes = 44 minutes

Total time: 3 hours 44 minutes

In general, if A can do a whole job in p time periods and B can do a job in q time periods, together they can do the job in time periods.

Answer by josmiceli(19441) (Show Source): You can put this solution on YOUR website!
You hav eto add their rates of working
In words:
(1 car repaired)/(T's time to repair) + (1 car repaired)/(J's time to repair)
= (1 car)/(combined times)

Multiply both sides by

hrs

Working together, it takes them 3 hrs and 44 min
This problem assumes a lot, and it's a good mental excercise
imagining why this answer might be wrong
Would they get in eachother's way fixing the car?
Do they get along with eachother?
Do they have to share tools?
Can they actually help eachother so much that
the time is less than expected
On and on and on, but I gave you the "expected" answer
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