Question 1159420
A person is rowing downstream. As he passes under a bridge, a bottle of vodka falls into the water.
 Since the bottle is 1/2 full, it floats, and he doesn't hear it.
 He continues to row. 
 After 20 minutes, he turns around to take another drink.
 He sees the bottle is gone, and assumes it fell into the water. 
 He turns around and rows upstream until he sees the bottle and retrieves it one (1) mile downstream from the bridge.
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What is the speed of the current?
:
The bottle is moving the speed of current, but the current is not involved with the relationship of boat and the bottle. therefore
If he rowed 20 min away from the bottle it will take him 20 min to row back to the bottle.
This took a total of 40 min, at which time the bottle has traveled 1 mi from the bridge. 
let s = the speed of the current. 40 min is 2/3 of an hr
{{{2/3}}}s = 1
2s = 3*1
s = {{{3/2}}}
s = 1.5 mph is the speed of the current