A train goes twice as fast downhill as it can go uphill, and 2/3 feet as fast uphill as it can go on level ground. if it goes 120 miles per hour downhill, how long will it take to travel 45 miles per flat land?

Given that the train goes twice as fast downhill as it can go uphill, and 2/3 feet as fast uphill as it can go on level ground.

If it goes 120 miles per hour downhill, then its speed uphill is 120 / 2 = 60 miles per hour and its speed on a flat land is 60 / (2/3) = (60 x 3) / 2 = 180 / 2 = 90 miles per hour.

Therefore, the amount of time it will take the train to travel 45 miles on flat land is given by 45 / 90 = 0.5 hours = 30 minutes.