Question 103082This question is from textbook
: A subway train makes six stops of equal length during its 21 km run. The train is actually moving for 20 mins of the trip. At most how long can the train remain at each station if the average speed for the trip, including stops, is to be at least 36km/hr?
This question is from textbook
Answer by oberobic(2304)   (Show Source):
You can put this solution on YOUR website! We are told d = distance traveled = 21 km.
We are told average speed = 36 km/hr.
The standard distance equation is: d = rt. We know r=36 and d=21, but we don't know t, so we find it by dividing d by r:
21/36=t
We can simplify 21/36 to be 7/12 of an hr.
We know an hour is 60 minutes and that 5*12=60, so 35 minutes must be the total time allowed to cover 21km to have an average speed of 36km/hr.
This is a good place to check your intermediate result.
Does rt = d? That is does 36*(35/60) = 21? Yes, it does.
We also are told the train is in motion for only 20 minutes. That means it is sitting in the station for 15 minutes.
We know there are 6 stops, but would we keep the timer running for the at the last stop. That is, would we stop the timer when we got to the last station or not? I assume we would. But I do not think we would count the station where we got onto the train as a stop...it was the start! (smile)
So, there actually were 5 stops along the way that took time. 15/5 = 3 minutes per stop (max).
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