SOLUTION: you drive to the store at 20 mph and return by the same route at 30 mph. Discounting the time spent at the store, what was your average speed?

Question 250787: you drive to the store at 20 mph and return by the same route at 30 mph. Discounting the time spent at the store, what was your average speed?
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
you drive to the store at 20 mph and return by the same route at 30 mph.
Discounting the time spent at the store, what was your average speed?
:
Let d = the one way distance
then
2d = the round trip
:
Let a = average speed
:
Write a time equation: time = dist/speed
:
Time there + time back = time there & back
+ =
multiply equation by 60a, results:
3da + 2da = 60(2d)
3da + 2da = 120d
:
divide thru by d, get rid of it
3a + 2a = 120
5a = 120
a =
a = 24 mph is the average speed
:
:
See if that is true:
Find the times if d = 60 mi
60/20 + 60/30 = 120/24
3 + 2 = 5

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