SOLUTION: Mary walks at 4 mph. sarah jogos 10 mph. if they both leave the school at 8 am going along the same path in the same direction, at what time will they be 9 miles apart?

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Question 737631: Mary walks at 4 mph. sarah jogos 10 mph. if they both leave the school at 8 am going along the same path in the same direction, at what time will they be 9 miles apart?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +d+ = Sarah's distance when they are 9 mi apart
+d+-+9+ = Mary's distance when they are 9 mi apart
Let +t+ = time in hrs passed after 8 AM when they are 9 mi apart
-------------
Sarah's equation:
(1) +d+=+10t+
Mary's equation:
(2) +d+-+9+=+4t+
------------
(2) +d+=+9+%2B+4t+
By substitution:
(2) +10t+=+9+%2B+4t+
(2) +6t+=+9+
(2) +t+=+3%2F2+'
8 AM + 3/2 hrs = 9:30 AM
check:
(1) +d+=+10%2A%283%2F2%29+
(1) +d+=+15+
and
(2) +d+-+9+=+4%2A%283%2F2%29+
(2) +d+=+9+%2B+6+
(2) +d+=+15+
OK