A certain river has a current of 3 miles per hour. A boat takes twice as long to travel upstream between two points as it does to travel downstream between the same two points. What is the speed of the boat in still water?
Solution
Correct Answer: Option C
Let Boat speed = x mph
current = 3 mph
against current speed = x-3
with current speed = x+3
let y be the distance .
downstream t= y/(x+3)............(1)
upstream 2t = y/(x-3)..............(2)
multiply (1) by (2) ,
2t=2y/(x+3)
Therefore y/(x-3)=2y/(x+3)
1/(x-3)=2/(x+3)
2(x-3)=x+3
2x-6=x+3
2x-x=6+3
x=9 mph speed of b
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