   SEARCH HOME Math Central Quandaries & Queries  Subject: uniform motion Name: bob Who are you: Other A motorboat can maintain a constant speed of 16 miles per hour relative to the water. The boat makes a trip upstream to a certain point in 20 minutes; the return trip takes 15 minutes. What is the speed of the current? Hello,

Use the fact that distance is velocity multiplied by time: d = v t.

The boat's velocity is going to be its velocity relative to the water, plus the velocity of the current.

d = (vboat + vcurrent) t

Let v be the velocity of the current downstream (you could pick upstream here, but I felt like picking downstream). Then the velocity of the current upstream (if we keep the boat's velocity at positive 16 miles per hour) is -v. The distance travelled going upstream is the same as the distance downstream.

From here can you set up an equation that lets you solve for v?

-Haley     Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.