SOLUTION: Mario and Julio are working together to detail cars. When they work together they can wash 7 cars in 2 hours. If Mario works alone he can detail 5 cars in 3 hours. If Julio works a

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Question 1013228: Mario and Julio are working together to detail cars. When they work together they can wash 7 cars in 2 hours. If Mario works alone he can detail 5 cars in 3 hours. If Julio works alone, how long will it take him to detail 12 cars?
Found 2 solutions by macston, ikleyn:
Answer by macston(5194) About Me  (Show Source):
You can put this solution on YOUR website!
Mario: 5 cars/3 hours=5/3 cars per hour
.
Together: 7 cars /2 hours
In 2 hours Mario details 2hrs(5/3 car/hr)=10/3 cars
.
7 cars-10/3 cars=21/3 cars-10/3 cars=11/3 cars
.
When working together for 2 hours, Mario details 10/3 cars, leaving 11/3 cars for Julio.
Thus Julio: 11/3 cars/2 hours=11/6 cars per hour.
.
For Julio to detail 12 cars:
12 cars /(11/6 cars/hr)=6.55 hours
.
ANSWER: It would take Julio 6.55 hours to detail 12 cars.

Answer by ikleyn(52903) About Me  (Show Source):
You can put this solution on YOUR website!
.
Mario and Julio are working together to detail cars. When they work together they can wash 7 cars in 2 hours.
If Mario works alone he can detail 5 cars in 3 hours. If Julio works alone, how long will it take him to detail 12 cars?
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Let m be Mario's rate when he works alone, and j be Julio's rate when he works alone. 

From the condition, 

m = 5%2F3 car%2Fhour,

m + j = 7%2F2 car%2Fhour.

Hence, j = (m+j) - m = 7%2F2+-+5%2F3 = 21%2F6+-+10%2F6 = 11%2F6 car%2Fhour

Therefore, if Julio works alone, it will take for him  12 : 11%2F6 = %2812%2A6%29%2F11 hour to wash 12 cars.