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When the friend left the beach, Lucy was (0.5 hours) * 50 mph = 25 mph ahead.
But the friend moves faster, decreasing the distance between them by 5 = 55 - 50 miles per hour.
So, the friend will catch Lucy in = 5 hours.
Algebra solution
Algebra solution is this equation
50*(t+0.5) = 55*t,
saying that both of them cover the same distance from the start to the catching point.
In this equation " t " is the time starting from the moment, when the friend began his move.
Simplify and solve it
50t + 25 = 55t
25 = 55t - 50t
25 = 5t
t = = 5 hours.
The same answer as in the very first solution.
Solved.
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See introductory lessons on Travel and Distance problems
- 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.
They are written specially for you.
You will find the solutions of many similar problems there.
Read them and learn once and for all from these lessons on how to solve simple Travel and Distance problems.
Become an expert in this area.
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Ignore the post by @josgarithmetic, since it is totally nonsensical.