Multiple choice

Suppose you walk from home to the bus stand at 4 km/h and immediately return at x km/h. If the average speed is 6 km/h, then x is

  1. 8 km/h

  2. 10 km/h

  3. 12 km/h

  4. Cannot be determined unless the distance from home to bus stand is known.
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C Correct answer
Explanation

Average speed = 2xy / (x+y). 6 = 2(4)(x) / (4+x) => 6(4+x) = 8x => 24 + 6x = 8x => 2x = 24 => x = 12.

AI explanation

When equal distances are traveled at two different speeds, the average speed is calculated using the harmonic mean formula: Average Speed = 2xy / (x + y). Substituting the known values gives 6 = (2 * 4 * x) / (4 + x), which simplifies to 24 + 6x = 8x. Solving this equation yields x = 12 km/h.

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