SOLUTION: The speed of a boat in still water is 15 km/hr. It goes 3 km upstream and returndownstream to the original point in 4 hrs 30 minutes.Find the speed of the stream.

Algebra ->  Finance -> SOLUTION: The speed of a boat in still water is 15 km/hr. It goes 3 km upstream and returndownstream to the original point in 4 hrs 30 minutes.Find the speed of the stream.      Log On


   

Question 1180672: The speed of a boat in still water is 15 km/hr. It goes 3 km upstream and returndownstream to the original point in 4 hrs 30 minutes.Find the speed of the stream.
Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


The numbers look unreasonable. Only 3km upstream and back in 4.5 hours means the speed of the stream must be nearly equal to the speed of the boat.

In any case....

x = speed of stream
15+x = downstream speed
15-x = upstream speed
3/(15+x) = downstream time
3/(15-x) = upstream time

The total time is 4.5 hours:

3%2F%2815%2Bx%29%2B3%2F%2815-x%29=4.5

With the suspicious numbers, I wouldn't even try solving that algebraically. I would graph the two functions 3%2F%2815%2Bx%29%2B3%2F%2815-x%29 and 4.5 on a graphing calculator and find where they intersect.

graph%28400%2C400%2C-1%2C15%2C-1%2C5%2C3%2F%2815%2Bx%29%2B3%2F%2815-x%29%2C4.5%29