Multiple choice

A boat goes upstream at a speed of 15 km/hr and comes back the same distance at 24 km/hr. What is the average speed (in km/hr) for the total journey?

  1. 17.4

  2. 18.5

  3. 19.3

  4. 18.9
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For equal distances at different speeds, average speed = 2ab/(a+b) where a=15, b=24. Average = 2×15×24/(15+24) = 720/39 = 18.46 km/hr, which rounds to 18.5. Option A (17.4) would be (15+24)/2 incorrectly. Option C (19.3) is too high. Option D (18.9) doesn't match the formula.

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