Answer:
- boat: 15 mph
- current: 5 mph
Explanation:
The relation between time, speed, and distance is ...
speed = distance/time
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The speed downstream is ...
downstream speed = (100 mi)/(5 h) = 20 mi/h
The speed upstream is ...
upstream speed = (100 mi)/(10 h) = 10 mi/h
The boat's speed in still water is the average of these:
boat speed = ((downstream speed) + (upstream speed))/2 = (20 +10)/2 mi/h
boat speed = 15 mi/h
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The speed of the current is the difference between the travel speed and the boat speed:
current speed = downstream speed - boat speed
= (20 mi/h) - (15 mi/h)
current speed = 5 mi/h