SOLUTION: Juan's boat will go 19 miles per hour in still water. If he can go 13 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed of the

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: Juan's boat will go 19 miles per hour in still water. If he can go 13 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed of the       Log On

Ad: Over 600 Algebra Word Problems at edhelper.com


   



Question 1007500: Juan's boat will go 19 miles per hour in still water. If he can go 13 miles downstream in the same amount of time as it takes to go 9 miles upstream, then what is the speed of the current?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +c+ = the speed of the current
+19+%2B+c+ = boat's speed going downstream in mi/hr
+19+-+c+ = boat's speed going upstream in mi/hr
Let +t+ = time in hrs going both
downstream and upstream
------------------------------------
equation for going downstream:
(1) +13+=+%28+19+%2B+c+%29%2At+
equation for going upstream:
(2) +9+=+%28+19+-+c+%29%2At+
---------------------------
(1) +t+=+13%2F%28+19+%2B+c+%29+
Substitute this result into (2)
(2) +9+=+%28+19+-+c+%29%2A%28+13+%2F+%28+19+%2B+c+%29%29+
(2) +9%2A%28+19+%2B+c+%29+=+13%2A%28+19+-+c+%29+
(2) +171+%2B+9c+=+247+-+13c+
(2) +22c+=+76+
(2) +c+=+3.455+
The speed of the current is 3.455 mi/hr
----------------------
check:
(1) +13+=+%28+19+%2B+c+%29%2At+
(1) +13+=+%28+19+%2B+3.455+%29%2At+
(1) +13+=+22.455t+
(1) +t+=+.579+ hrs
--------------------
(2) +9+=+%28+19+-+c+%29%2At+
(2) +9+=+%28+19+-+3.455+%29%2At+
(2) +9+=+15.545t+
(2) +t+=+.579+ hrs
OK