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 Question from Lloyd, a student: A boat travelled 210 miles downstream and back. The trip downstream took 10hrs, the trip back took 70hrs 1. what is the speed of the current? 2. what is the speed of the boat in still water?

Hi Lloyd,

The solution to this problem depends on three facts. First of all rate equals distance divided by time. In your case you have distance in miles and time in hours so the rate will be in miles per hour. This fact will allow you to calculate the rate at which the boat travels upstream and the rate at which it travels downstream.

When the boat is travelling downstream, with the current, the current helps push the boat along and the rate at which the boat travels is the rate it travels in still water plus the rate of the current. When the boat is travelling upstream, against the current, the current holds the boat back and the rate at which the boat travels is the rate it travels in still water minus the rate of the current. These latter two facts along with the results you obtained from the first fact allow you to write two equations with variables "the speed of the boat in still water" and "the speed of the current". Solve these two equation for their variables.

Write back if you need more assistance,
Penny

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