Multiple choice

The uniform speed Of a motorboat in upstream is 12 km per hour and its downstream speed is 18 km per hour. The motorboat goes from point P to point Q in upstream and returns the same distance in downstream. What is its average speed of the entire journey? (the speed Of the motorboat and stream was uniform during the entire journey)

  1. 15 km hour

  2. 14.8 km per hour

  3. 14.2 km per hour

  4. 14.4 km per hour
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D Correct answer
Explanation

Average speed for a round trip is 2xy / (x+y), where x and y are the upstream and downstream speeds. Average speed = 2 * 12 * 18 / (12 + 18) = 432 / 30 = 14.4 km/hr.

AI explanation

Use the average speed formula for equal distances: (2 multiplied by upstream speed multiplied by downstream speed) divided by (upstream speed plus downstream speed). Substituting the given values gives (2 multiplied by 12 multiplied by 18) divided by (12 plus 18). This calculates to 432 divided by 30, which equals 14.4 kilometers per hour.

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