SOLUTION: If I travel for one hour from my house to my friend's house at a rate of 9mph on flat ground, 6mph when the terrain is uphill and 18mph when the terrain is downhill, how many miles

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It's not real clear, but I assume the whole trip
takes 1 hr.
Let = time for the portion on flat ground
Let = distance for the portion on flat ground
Let = time for uphill portion
Let = distance for the uphill portion
Let = time for downhill portion
Let = distance for the downhill portion
given:
(1) hr
(2)
(3)
(4)
--------------------
What I need to find is
Rewrite (2),(3) and (4) like this:
(2)
(3)
(4)
Add the 3 equations


Write the left side with as denominators

If ,
and ,

The left side is

mi
It is 11 miles between houses
check answer:
(2)
(2)
(3)
(3)
(4)
(4)
(1) hr
(1) hr