A fisherman travels downstream at full speed to his favorite fishing spot. The stream is running at a rate of 5 miles per hour, and he takes an hour to get to the fishing hole. He catches 5 fish and calls it a day. He takes twice as long at full speed to get back to the dock going against the current. How fast will his fishing boat go?

Question

anonymous · Answer

Now you can say that, going there, his speed was x (fastest speed) +5. Now on the way back, it was x-5. Now the difference in his speed is 10mph. If it took him twice as long to get back, then the only possible answer is that he was going 20mph there with a +5 current and 10mph back with a -5 current, giving you a top speed of 15mph.