Question 941509
Perry goes for a 3 hour trip through town and country roads.
 If she averages 55mph on country roads and 35 mph through the towns, and if she travels 3 times as far on country roads as she does through towns, what is the total length of her trip?
:
Let d = distance traveled in town
then
3d = distance traveled on country roads
and
4d = total distance traveled
:
Write a time equation; time = dist/speed
:
Town travel time + country travel time = 3 hrs
{{{d/35}}} + {{{(3d)/55}}} = 3
multiply equation by the LCM of 35 & 55, namely 1925
1925*{{{d/35}}} + 1925*{{{(3d)/55}}} = 3(1925)
Cancel the denominators
55d + 35(3d) = 5775
55d + 105d = 5775
160d = 5775
d = 5775/160
d = 36.1 mi in the town
we know 4d = total distance
4(36.1) = 144.4 mi the length of the trip
:
:
Check this by finding the actual times
36.1/35 = 1.03 hrs
3(36.1)/55 = 1.97 hrs
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total travel time: 3 hrs