Multiple choice

It takes a boat 3 hr to travel 27 km upstream. The same boat can travel 30 km downstream in 2 hr. Find the speed of the boat and the current.

  1. 12 km/hr, 6 km/hr

  2. 11 km/hr, 3 km/hr

  3. 12 km/hr, 3 km/hr

  4. 10 km/hr, 5 km/hr
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let b be boat speed and c be current speed. Upstream: b - c = 27/3 = 9. Downstream: b + c = 30/2 = 15. Adding the equations gives 2b = 24 (b = 12), and subtracting gives 2c = 6 (c = 3).

AI explanation

The upstream speed is 27 km / 3 hr = 9 km/hr and the downstream speed is 30 km / 2 hr = 15 km/hr. The speed of the boat in still water is half the sum of these speeds, meaning (15 + 9) / 2 = 12 km/hr. The speed of the current is half the difference, meaning (15 - 9) / 2 = 3 km/hr. The result is 12 km/hr for the boat and 3 km/hr for the current.

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