SOLUTION: The speed of a stream is 4 mph. If a boat travels 52 miles downstream in the same time that it takes to travel 26 miles upstream, what is the speed on the boat in still water?

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Question 28317: The speed of a stream is 4 mph. If a boat travels 52 miles downstream in the same time that it takes to travel 26 miles upstream, what is the speed on the boat in still water?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
The thing that stays the same for both trips is elapsed time
Solve the rate formula for t
time = distance / rate
The times are equal, so
distance%5B1%5D+%2F+rate%5B1%5D+=+distance%5B2%5D+%2F+rate%5B2%5D
The rate for downstream is the rate in still water + rate of the current
The rate for upstream is the rate in still water - rate of the current
Fill in the values
Call the rate in still water r
52+%2F+%28r+%2B+4%29+=+26+%2F+%28r+-+4%29
Cross multiply
26%2Ar+%2B+104+=+52%2Ar+-+208
26%2Ar+=+312
r+=+12
So, the speed in still water is 12 mph
Check by plugging into equation
52+%2F+%2812+%2B+4%29+=+26+%2F+%2812+-+4%29
52+%2F+16+=+26+%2F+8
13%2F4+=+13%2F4
Checks