Multiple choice

A train covers a distance from station A to station B at a uniform speed of 60 km/hr and returns to station A at a uniform slower speed. If the average speed for the whole trip be 48 km/hr, then what is the return speed of the train?

  1. 46.8 km/hr

  2. 40 km/hr

  3. 54 km/hr

  4. 52 km/hr
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B Correct answer
Explanation

Average speed for a round trip is 2xy / (x + y), where x and y are the speeds. 48 = 2 * 60 * y / (60 + y). 48(60 + y) = 120y => 2880 + 48y = 120y => 72y = 2880 => y = 40.

AI explanation

Using the average speed formula for equal distances, Average Speed equals twice the product of the two speeds divided by their sum, which is 2 times S1 times S2 divided by S1 plus S2. Let the return speed be x, so 48 equals 2 times 60 times x divided by 60 plus x. This simplifies to 48 times 60 plus 48x equals 120x, meaning 2880 equals 72x. Solving for x gives a return speed of 40 km/hr.

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