Question 70

A car travels a certain distance at 32 km/h and comes back at 68 km/h. What is the average speed for total journey?

Solution

Average speed of the journey is the harmonic mean of the speeds 32 and 68 km/hr

Harmonic mean of two numbers 'x' and 'y' = $$\frac{2}{\frac{1}{x} + \frac{1}{y}}$$

Average speed = $$\frac{2}{\frac{1}{32} + \frac{1}{68}}$$

= $$2 \div {\frac{68 + 32}{68 \times 32}} = \frac{2 \times 68 \times 32}{100}$$

= $$\frac{4352}{100} = 43.52$$ km/hr

=> Ans - (C)

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