SOLUTION: A worker drove to work traveling 65 miles per hour. He returned home traveling 55 miles per hour. What was his average speed if the entire trip took 4 hours?

Question 188738: A worker drove to work traveling 65 miles per hour. He returned home traveling 55 miles per hour. What was his average speed if the entire trip took 4 hours?
Found 2 solutions by Alan3354, Edwin McCravy:
Answer by Alan3354(69443) (Show Source): You can put this solution on YOUR website!
A worker drove to work traveling 65 miles per hour. He returned home traveling 55 miles per hour. What was his average speed if the entire trip took 4 hours?
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d = rt
t = d/r
4 = d/55 + d/65
4 = (13d + 11d)/715
24d = 2860
d = 119 1/6 miles each way
r (avg) = 2d/4
r = 59 5/6 mph
Answer by Edwin McCravy(20062) (Show Source): You can put this solution on YOUR website!
Alan made a slight error!
Edwin's solution:
A worker drove to work traveling 65 miles per hour. He returned home traveling 55 miles per hour. What was his average speed if the entire trip took 4 hours?

Suppose the distance between his home and his word is miles. Then his total distance is miles Using His time going to work = His time returning home = Therefore his The LCD is 715, so we multiply that fraction by but we write it as miles per hour Notice three things here: 1. We did not even use the 4 hours! 2. The distance N miles between his home and work canceled out. This means that the time and the distance are independent of the average speed. 3. Important! To find the average speed, it does not work to just average the two speeds! For that would have been 60 mph not mph. Edwin

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