Question 1134504
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If the times are the same, then the ratio of distances is the same as the ratio of speeds.<br>
Let c be the speed (mph) of the current.  Since the boat's speed in still water is 16, the upstream and downstream speeds are 16-c and 16+c.  Then, since the boat can go 15mi downstream in the same time is can go 9mi upstream,<br>
{{{(16+c)/(16-c) = 15/9 = 5/3}}}
{{{80-5c = 48+3c}}}
{{{32 = 8c}}}
{{{c = 4}}}<br>
The speed of the current is 4mph.