Question
Fri October 26, 2012 By: Ashrene

a boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream.if the speed of the boat in still water is 10mph then the speed of the stream is ?

Expert Reply
Fri October 26, 2012

Let the speed of the stream x mph. Then,

Speed downstream = (10 + x) mph,

Speed upstream = (10 - x) mph.

=> [36 / (10-x)] - [36 / (10+x)] = 90/60    { to convert 90 mins into hr = 90/60 hr}

=> 72x * 60 = 90 (100 - x2)

=> x2 + 48x - 100 = 0

=> (x+ 50)(x - 2) = 0

=> x = 2 mph Answer . since x = -50 is not valid here

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