Math CentralQuandaries & Queries


Question from Shayan, a student:

A boat is traveling 20 miles per hour when it passes a lighthouse.
another boat is traveling at 15 miles per hour when it passes a point.
the lighthouse and the point are 175 miles apart.
when will the boats pass each other?

Hi Shayan,

I assume the boats are travelling towards each other. The first boat is travelling at 20 mph toward the second and the second boat is travelling at 15 mph towards the first. At what rate is the distance between them decreasing? At this rate how long does it take for the distance to decrease from 175 miles to zero miles?


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