SOLUTION: A goes down river 9 miles, then back upriver for 3 miles. Rate of river current is 6 mph. How long does it take A to go the 12 miles? I have 9/x-6 for time downstream, and 3/x-6

Algebra ->  Expressions-with-variables -> SOLUTION: A goes down river 9 miles, then back upriver for 3 miles. Rate of river current is 6 mph. How long does it take A to go the 12 miles? I have 9/x-6 for time downstream, and 3/x-6      Log On


   

Question 674338: A goes down river 9 miles, then back upriver for 3 miles. Rate of river current is 6 mph. How long does it take A to go the 12 miles? I have 9/x-6 for time downstream, and 3/x-6 for time upstream, but don't know how to set up the equation. (Answer is 1 hour.)
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
let +r+ = A's rate in still water ( no current )
Going downstream, his rate is +r+%2B+6+
Going upstream, his rate is +r+-+6+
---------------
Going downstream,
+9+=+%28+r+%2B+6+%29%2At%5B1%5D+
Going upstream,
+3+=+%28+r+-+6+%29%2At%5B2%5D+
-------------------
You need to find +t%5B1%5D+%2B+1%5B2%5D+
+t%5B1%5D+=+9+%2F+%28+r+%2B+6+%29+
+t%5B2%5D+=+3+%2F+%28+r+-+6+%29+
--------------------
+t%5B1%5D+%2B+t%5B2%5D+=+9%2F%28+r+%2B+6+%29+%2B+3%2F%28+r+-+6+%29+
I think you're missing his rate in still water
Can't solve without it.