SOLUTION: Candy drives to class in 30 minutes. By averaging 10 mph more, her roommate Fran drives to the same class in 20 minutes. What is Candy's average speed?

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Question 781953: Candy drives to class in 30 minutes. By averaging 10 mph more, her roommate Fran drives to the same class in 20 minutes. What is Candy's average speed?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = her average speed in mi/hr
Candy's equation:
+d+=+s%2A%2830%2F60%29+ ( time in hours )
Fran's equation:
+d+=+%28+s%2B10+%29%2A%2820%2F60%29+
----------------------------
By substitution:
+%281%2F2%29%2As+=+%281%2F3%29%2A%28+s%2B10+%29+
+3%2A%281%2F2%29%2As+=+s+%2B+10+
+%283%2F2%29%2As+-+s+=+10+
+%281%2F2%29%2As+=+10+
+s+=+20+
Candy's average speed is 20 mi/hr
check:
+d+=+s%2A%2830%2F60%29+
+d+=+20%2A%2830%2F60%29+
+d+=+10+ mi
and
+d+=+%28+s%2B10+%29%2A%2820%2F60%29+
+d+=+%28+20%2B10+%29%2A%281%2F3%29+
+d+=+10+ mi
OK