SOLUTION: Aubry's boat goes 20 mph in still water. It travels 75 miles upstream and back in a total time of 8 hours. What is the speed of the current?

Algebra ->  Functions -> SOLUTION: Aubry's boat goes 20 mph in still water. It travels 75 miles upstream and back in a total time of 8 hours. What is the speed of the current?      Log On


   

Question 132577: Aubry's boat goes 20 mph in still water. It travels 75 miles upstream and back in a total time of 8 hours. What is the speed of the current?
Answer by mathispowerful(115) About Me  (Show Source):
You can put this solution on YOUR website!
Since total time is 8 hours:

If we let x be the current speed, the upstream speed is
20-x, downstream speed is 20+x
So 75%2F%2820-x%29%2B75%2F%2820%2Bx%29=8
Multiply (20-x)(20+x) on both sides:
75(20+x)+75(20-x)=8(20-x)(20+x)
simplify it we get:
3000=8%28400-x%5E2%29
3000+=+3200-8x%5E2
That is 8x%5E2=3200-3000
8x%5E2=200
x%5E2=25
x=5
So the answer is 5 miles/hr.