Question 1208940
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The solution method  from the other tutor is fine, and it is probably what you will find in most references.<br>
Usually, when the distances are the same at two different speeds, the algebra required to find the answer is easier if you use the fact that the speed is inversely proportional to the time.  A solution using that starting point is shown below.<br>
Let x be the speed of the current.  Then the upstream speed is 16-x and the downstream speed is 16+x.<br>
The distances upstream and downstream are the same.  Then, since the ratio of times upstream and downstream is 20:15 = 4:3, the ratio of the upstream and downstream speeds is 3:4.  So<br>
{{{(16-x)/(16+x)=3/4}}}
{{{3(16+x)=4(16-x)}}}
{{{48+3x=64-4x}}}
{{{7x=16}}}
{{{x=16/7}}}<br>
ANSWER: 16/7 mph, or 2 2/7 mph<br>