SOLUTION: Please help! susan left her home at 7:00 am, driving her car at a rate of 45 mph. at 9:00 am her sister marion drove after her along the same highway traveling at the rate of 60 m

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Question 517969: Please help!
susan left her home at 7:00 am, driving her car at a rate of 45 mph. at 9:00 am her sister marion drove after her along the same highway traveling at the rate of 60 mph. in how many hours did marion pass susan?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
How much of a head start in miles did Susan get?
+d%5B1%5D+=+45%2A2+ ( from 7 to 9 is 2 hours )
+d%5B1%5D+=+90+ mi
Start a stopwatch when Marion leaves.
Now they each will travel different distances
for the same amount of time.
Let d = the distance that Marion travels
----------
Susan's equation:
(1) +d+-+90+=+45t+
Marion's equation:
(2) +d+=+60t+
Substitute (2) into (1)
(1) +60t+-+90+=+45t+
(1) +15t+=+90+
(1) +t+=+6+
Marion will pass Susan in 6 hours
check:
(2) +d+=+60t+
(2) +d+=+60%2A6+
(2) +d+=+360+
and
(1) +d+-+90+=+45t+
(1) +360+-+90+=+45t+
(1) +270+=+45t+
(1) +t+=+6+
OK