SOLUTION: A red car is traveling at 55 mph. A blue car is traveling at 65 mph. The cars are 305 miles apart. The cars started at the same spot at different times. The cars have been driving

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Question 737528: A red car is traveling at 55 mph. A blue car is traveling at 65 mph. The cars are 305 miles apart. The cars started at the same spot at different times. The cars have been driving for 5 hours. Which system of equations could be used to solve for the total driving time of the red car (r) and the total driving time of the blue car (b)?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +d+ = distance red car has traveled
+305+-+d+ = distance blue car has traveled
+r+ = time for red car
+b+ = time for blue car
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One of the cars must have been traveling for
+5+ hrs, the other for less time
-----------------------
red car:
(1) +d+=+55%2Ar+
blue car:
(2) +305+-+d+=+65%2Ab+
---------------------
(2) = +d+=+305+-+65b+
By substitution:
+55r+=+305+-+65b+
+11r+%2B+13b+=+61+
The red car had to be the one traveling for +5+,
since +13%2A5+=+65+ is too much, so
+11%2A5+%2B+13b+=+61+
+13b+=+61+-+55+
+13b+=+6+
+b+=+6%2F13+ hrs
The red car drove for 5 hrs, the blue car drove for 6/13 hrs
check:
(1) +d+=+55%2Ar+
(1) +d+=+55%2A5+
(1) +d+=+275+
and
(2) +305+-+d+=+65%2Ab+
(2) +305+-+275+=+65%2A%286%2F13%29+
(2) +30+=+30+
OK