<PRE><B>Question 1205975</B>
Josh can clean the math building on his campus in 3 hours. Ken takes 7 hours to clean the same building. If they work​ together, how long will it take them to clean this​ building?

Josh can clean the math building on his campus in 3 hours

Assune cleaning the building as one job,

So josh can do 1/3 of the job in 1 hour.

Ken takes 7 hours to clean the same building.

So he does 1/7th of the job in 1 hour

If they work together they do (1/3 +1/7 ) of the job in 1 hour

= 10/21 of the job in 1 hour

Therefore to complete the job  together they take 21/10 hours = 2.1 hours.






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