Answer: 20 hours
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One way to solve
1 car = 20 minutes
3*(1 car) = 3*(20 minutes) multiply both sides by 3
3 cars = 60 minutes
3 cars = 1 hour
20*(3 cars) = 20*(1 hour) ... multiply both sides by 20
60 cars = 20 hours
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Another way to solve
(1 car)/(20 minutes) = (60 cars)/(x minutes)
1/20 = 60/x
1*x = 20*60 ... cross multiply
x = 1200 minutes
x = (1200 min)*( (1 hr)/(60 min) )
x = (1200/60) hr
x = 20 hours
