Multiple choice

If half of a distance is covered at a speed of 5 km/hr and the rest is covered at a speed of 15 km/hr, then what is the average speed?

  1. 10 km/hr

  2. 2.5 km/hr

  3. 7.5 km/hr

  4. 20 km/hr
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C Correct answer
Explanation

Average speed for equal distances is 2*v1*v2 / (v1+v2). Here, 2 * 5 * 15 / (5 + 15) = 150 / 20 = 7.5 km/hr.

AI explanation

Use the harmonic mean formula for average speed when equal distances are traveled at different speeds, which is 2xy divided by (x + y). Substituting the given speeds of 5 km/hr and 15 km/hr, we get 2 multiplied by 5 multiplied by 15, divided by the sum of 5 and 15. This calculates to 150 divided by 20, resulting in an average speed of 7.5 km/hr.

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