<PRE><B>Question 698045</B>
If you start out a 395 mile trip setting your cruise control to a constant speed of 70 mph, how many hours into the trip do you need to kick it up to 75 mph in order to arrive at your destination in exactly 5.5 hours?
:
Let t = travel time until you must increase speed to 75
then
(5.5-t) = time traveling at 75 mph
:
Write a distance equation
75(5.5-t) + 70t = 395
412.5 - 75t + 70t = 395
-5t = 395 - 412.5
5t = 17.5
t = 17.5/5
t = 3.5 hrs travel time when speed is increase to 75
:
:
Confirm this, find the distance at each speed
75*2 = 150 mi
70*3.5 = 245 mi
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total dist: 395 mi</PRE>