Hi,

I'm trying to solve this problem:

Phyllis is navigating her boat upstream in the Orinoco River. She plans to do a roundtrip voyage, heading back to where she began after circling around a buoy upstream. The speed of the current is 3 miles per hour. If Phyllis’ boat can travel 16 miles per hour in still water, how long does it take her to make her trip if the buoy is 2 miles from her starting point?

If I use my common sense, I would say that it takes Phyllis 15 minutes, because any time added going upstream would be made up for going downstream, so I could just solve this problem using 10mph as my rate:

t=d/r, t=4/16=1/4hr

But, if I break it down, calculating for the time on each individual leg of the trip, I get:

Upstream

r=16-3=13

Therefore,

t=d/r, t=2/13=approx 0.154

Downstream

t=d/r, r=16+3=19

Therefore,

t=d/r, t=2/19=approx 0.105

Total time = 0.154+0.105 = approx 0.259, which is a tad over 15 minutes.

Please help! Why do I get different answers?

Ara