Question

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 10 mph, the speed of the stream is:

Answer 1

Let x miles per hr be the speed of the stream; Speed of boat in still water is given as 10mph So,

Speed of boat downstream = 10+x mph

Speed of boat upstream = 10-x mph

36/(10-x) - 36/(10+x) = 90/60

72x*60 = 90(100-x^2)

x^2 + 48x - 100 = 0

(x+50)(x-2) = 0

Hence, x(Speed of stream) = 2mph