SOLUTION: Kris drove part of a 185 mile trip at 50 mph and the rest at 55 mph. Find the distance she traveled at 50 mph if her total driving time was 3 hours and 30 minutes.

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Question 164494: Kris drove part of a 185 mile trip at 50 mph and the rest at 55 mph. Find the distance she traveled at 50 mph if her total driving time was 3 hours and 30 minutes.
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
Kris drove part of a 185 mile trip at 50 mph and the rest at 55 mph. Find the distance she traveled at 50 mph if her total driving time was 3 hours and 30 minutes.
:
Let d = distance traveled at 50 mph
Then the rest would be:
(185-d) = distance traveled at 55 mph
:
Change 3 hr 30 min to 3.5 hrs
:
Write a time equation: Time = dist%2Fspeed
:
Time at 50 mph + time at 55 mph = 3.5 hrs
d%2F50 + %28%28185-d%29%29%2F55 = 3.5
:
Multiply equation by a common denominator 50*55 = 2750
2750*d%2F50 + 2750*%28%28185-d%29%29%2F55 = 2750(3.5)
Cancel the denominators, results
55d + 50(185-d) = 9625
:
55d + 9250 - 50d = 9625
;
55d - 50d = 9625 - 9250
:
5d = 375
d = 375%2F5
d = 75 mi at 50 mph
;
:
Check solution by finding the time at each speed
(185-75)/55 = 2hr
75/50 = 1.5 hrs; adds up to 3.5 hrs