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: 

a) 2 mph 

b) 2.5 mph 

c) 3 mph 

d) 4 mph

Answer 1

Correct option: a) 2 mph

Explanation:

Let the speed of the stream be x hrs. Then, speed downstream=(4/x) kmph, speed upstream=(3/x) kmph; therefore(48/(4/x))+(48/(3/x))=14 or x=1/2

Speed downstream= 8 kmph and speed upstream= 6 kmph and rate of the stream=1/2*(8-6) kmph= 1 kmph