Question 156250
A subway train makes six stops of equal length during its 21 km run. The train is actually moving for 20 min 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 36 km/h
:
Convert 20 min to {{{1/3}}} hr
:
Let s = duration of the stop in hrs
:
Write a speed equation: speed = {{{dist/time}}}
:
{{{21/((6s+(1/3)))}}} => 36
:
21 => 36(6s+{{{1/3}}})
21 => 216s + 12
;
21 - 12 => 216s
:
216s <= 9
Convert hrs to minutes
s <= {{{9/216}}} * 60
s <= 2.5 min per stop to average 36 km.hr or greater
:
Check solution
Total time 6(2.5) + 20 = 35 min
:
Find the distance
{{{35/60}}} * 36 = 21 km confirms our solution