SOLUTION: A jet ski with average speed of 60 mph left a pier by the river upstream. Fifteen minutes after its motor broke, and it began drifting downstream for 3 hours and 45 minutes until r

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: A jet ski with average speed of 60 mph left a pier by the river upstream. Fifteen minutes after its motor broke, and it began drifting downstream for 3 hours and 45 minutes until r      Log On


   

Question 1133091: A jet ski with average speed of 60 mph left a pier by the river upstream. Fifteen minutes after its motor broke, and it began drifting downstream for 3 hours and 45 minutes until reached another pier, which was 2 miles away down the river from the original pier. What is the rate of the current, in mph?
Answer by ikleyn(52809) About Me  (Show Source):
You can put this solution on YOUR website!
.
Let the rate of the current be "x" miles per hour.

Then the speed of the jet ski upstream is (60-x) mph.


Moving  1%2F4 of an hour upstream, it covered the distance  %281%2F4%29%2A%2860-x%29  miles.


Then it moved downstream with the speed equal to the rate of the current x mph during  33%2F4 hours = 15%2F4 hours 

and covered the distance  %2815%2F4%29%2Ax downstream.


We are given that  


    %2815%2F4%29%2Ax = %281%2F4%29%2A%2860-x%29 + 2.


It is your basic equation.

To solve it, multiply first both sides by 4; then simplify step by step:


    15x = 60-x + 8

    15x + x = 60 + 8

    16x = 68  ==============>  x = 68%2F16 = 17%2F4.


ANSWER.  The rate of the current is  17%2F4 = 41%2F4 miles per hour.