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 ?
Asked by Ashrene | 26th Oct, 2012, 05:50: PM
Expert Answer:
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
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
Answered by | 26th Oct, 2012, 06:22: PM
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