Boats and streams
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See all →- A boat goes 30 km downstream in 2 hours and 18 km upstream in 2 hours. What is the speed of the stream? Answer: B. 3 km/h Answer: (B) 3 km/h Downstream speed = 15 km/h, upstream speed = 9 km/h. Stream speed = 15 - 9/2 = 3 km/h (boat speed = 12... 1
- The speed of a boat in still water is 15 km/h and the speed of the stream is 3 km/h. The boat goes 36 km downstream and comes back to the starting point. What is the total time taken (in hours)? Answer: C. 5 Answer: (C) 5 Downstream speed = 18 km/h (2 h), upstream speed = 12 km/h (3 h). Total = 5 hours. 1
- A boat covers 48 km downstream in 3 hours and 32 km upstream in 4 hours. What is the speed of the boat in still water (in km/h)? Answer: B. 12 Answer: (B) 12 Downstream speed = 16 km/h, upstream = 8 km/h. Speed in still water = (16 + 8) ÷ 2 = 12 km/h. 1
- A boat takes 3 hours more to travel 45 km upstream than to travel 45 km downstream. If the speed of the stream is 2 km/h, what is the speed of the boat in still water? Answer: D. 8 km/h Answer: (D) 8 km/h Let the boat's speed be b. 45/b - 2 - 45/b + 2 = 3 ⇒ 180/b² - 4 = 3 ⇒ b² = 64 , b = 8 km/h. Check: upst... 1