If a boat goes upstream at a speed of 24 km/hr and comes back the same distance at 40 km/hr. What is the average speed (in km/hr) for the total journey?
30
For equal distances at speeds \(v_1\) and \(v_2\), the average speed is the harmonic mean:
\[\bar v=\frac{2v_1 v_2}{v_1+v_2}=\frac{2\times 24\times 40}{24+40}=\frac{1920}{64}=30\]
Therefore the average speed is 30 km/hr.
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