A jet boat is used to take canoers 200 miles upriver to their starting point. As the driver of the jet boat, Jeremy knows that it will take him 5 hours to get the canoers upstream, but only 4 hours to get the boat back downstream after dropping the canoers off, as long as he keeps the boat moving at a constant speed.

How fast would the boat be moving in still water?
A.
5 mph
B.
40 mph
C.
45 mph
D.
50 mph

Question

A jet boat is used to take canoers 200 miles upriver to their starting point. As the driver of the jet boat, Jeremy knows that it will take him 5 hours to get the canoers upstream, but only 4 hours to get the boat back downstream after dropping the canoers off, as long as he keeps the boat moving at a constant speed.  

How fast would the boat be moving in still water?
A.
5 mph
B.
40 mph
C.
45 mph
D.
50 mph

anonymous · Answer

200/5 = 40 mph 

200/4 = 50 mph 
Let x be the speed in still waters and y the speed of current. 


x + y = 50 

x - y = 40 

ADD 2x = 90 

x = 45 mph 

answer: C