SOLUTION: Rosie and Jack both drive the same distance to the shore. By driving 20 miles per hour faster than Jack, Rosie can get there in 3 hours while it takes Jack 4 hours. How fast does e

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Question 563260: Rosie and Jack both drive the same distance to the shore. By driving 20 miles per hour faster than Jack, Rosie can get there in 3 hours while it takes Jack 4 hours. How fast does each of them drive?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = Jack's speed in mi/hr
Let +d+ = distance to shore in miles
------------
given:
Rosie's equation:
(1) +d+=+%28+s+%2B+20+%29%2A3+
Jack's equation:
(2) +d+=+s%2A4+
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Substitute (2) into (1)
(1) +4s+=+%28+s+%2B+20+%29%2A3+
(1) +4s+=+3s+%2B+60+
(1) +s+=+60+
and
+s+%2B+20+=+80+
Rosie's speed is 80 mi/hr
Jack's speed is 60 mi/hr
check answer:
(1) +d+=+%28+s+%2B+20+%29%2A3+
(1) +d+=+80%2A3+
(1) +d+=+240+
and
(2) +d+=+s%2A4+
(2) +d+=+60%2A4+
(2) +d+=+240+
OK