Multiple choice

A boat goes 15 km/hr along the flow and 9 km/hr against the flow. What will be the speed of the boat in still water (in km/hr)?

  1. 3

  2. 6

  3. 12

  4. 24
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Let v be the speed in still water and c be the speed of the current. Downstream speed is v + c = 15 and upstream speed is v - c = 9. Adding the two equations gives 2v = 24, so v = 12.

AI explanation

Using the boat and stream formula, the speed of the boat in still water is half the sum of its downstream and upstream speeds. Adding the given speeds gives 15 plus 9, which equals 24 km/hr. Dividing this total by 2 gives a still water speed of 12 km/hr.

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