.
The "distance" equation
11*(r-18) = 8*r, (saying that the distance in both ways is the same)
where "r" is the average speed on the return drive (which is under the question).
11r - 11*18 = 8r ====> 11r - 8r = 11*18 ====> 3r = 11*18 ====> r = = 66.
Answer. The average speed on the return trip was 66 miles per hour.
Solved.
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To see other similar introductory Travel and Distance problems, see the lessons
- Travel and Distance problems
- Travel and Distance problems for two bodies moving in opposite directions
- Travel and Distance problems for two bodies moving in the same direction (catching up)
in this site.