Question 89

A car travels a certain distance at 34 km/h and comes back at 66 km/h. What is the average speed for total journey?

Solution

Average speed of the journey is the harmonic mean of the speeds 34 and 66 km/hr

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

Average speed = $$\frac{2}{\frac{1}{34} + \frac{1}{66}}$$

= $$2 \div {\frac{66 + 34}{66 \times 34}} = \frac{2 \times 66 \times 34}{100}$$

= $$\frac{4488}{100} = 44.88$$ km/hr

=> Ans - (D)

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