a) It takes a groundskeeper 45 minutes to prepare a softball field for a game. It takes his assistant 50 minutes to prepare the same field. How long will it take if they work together to prepare the field?
G does 1/45 job per minute
A does 1/50 job per minute
Together, they do 1/45 + 1/50 = 19/450 jobs/minute
--> 450/19 minutes to do the job
You can use a shortcut, product/sum
50*45/(50+45) = 2250/95
= 450/19
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b) It takes the owner/operator of a dog kennel 7 hours to clean all of the cages. It takes his assistant 4 hour(s) more than that to clean the same cages. How long will it take if they work together?
This is 7 and 11 hours.
7*11/(7+11) = 77/18 hours
= ~ 4.28 hours
