Solution:
For equal distances covered in two halves of a journey, average speed is \(v_{\text{avg}} = \frac{2v_1v_2}{v_1+v_2}\). Here, \(v_{\text{avg}} = \frac{2 \times 20 \times 40}{20+40} = \frac{80}{3}\text{ ms}^{-1}\).
A body moves from A to B with a constant speed of \(20\text{ ms}^{-1}\) and returns from B to A with a constant speed of \(40\text{ ms}^{-1}\). The average speed of the body for the whole journey is
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