SOLUTION: Tommy and Lisa leave their houses traveling in opposite direction on a straight road. Tommy drives 15 mph faster than Lisa. After 3 hours they are 225 miles apart. Find each rate

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Question 1049465: Tommy and Lisa leave their houses traveling in opposite direction on a straight road. Tommy drives 15 mph faster than Lisa. After 3 hours they are 225 miles apart. Find each rate
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = Lisa's speed in mi/hr
+s+%2B+15+ = Tommy's speed in mi/hr
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Think of this as one of them standing still
and the other one moving at the sum of their speeds
+225+=+%28+s+%2B+s+%2B+15+%29%2A3+
+%28+2s+%2B+15+%29%2A3+=+225+
+6s+%2B+45+=+225+
+6s+=+180+
+s+=+30+
and
+s+%2B+15+=+45+
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Tommy's speed is 45 mi/hr
Lisa's speed is 30 mi/hr
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check:
+d%5B1%5D+=+30%2A3+
+d%5B1%5D+=+90+ mi
and
+d%5B2%5D+=+45%2A3+
+d%5B2%5D+=+135+ mi
--------------------
+d%5B1%5D+%2B+d%5B2%5D+=+90+%2B+135+
+d%5B1%5D+%2B+d%5B2%5D+=+225+ mi
OK