Traveling 36 miles downstream takes 90 minutes shorter than travelling the same distance upstream. If the boat's speed on still water is 10 mph, the stream's speed is:
A. 2 mph
B. 2.5 mph
C. 3 mph
D. 4 mph
Answer:A
Traveling 36 miles downstream takes 90 minutes shorter than travelling the same distance upstream. If the boat's speed on still water is 10 mph, the stream's speed is:
A. 2 mph B. 2.5 mph C. 3 mph D. 4 mph
Explanation: Set the stream's speed to x mph. Then,Downstream speed = (10 + x) mph,Upstream speed equals (10 - x) mph.90/60 = 36/(10 - x) - 36/(10 + x),90 = 72x x 60 (100 - x2),0 = x2 + 48x - 100,0 = (x + 50)(x - 2),2 mph = x.