A car travels a certain distance at 70 km/h and comes back at 30 km/h. Find the average speed for total journey.
Average speed of the journey is the harmonic mean of the speeds 70 and 30 km/hr
Harmonic mean of two numbers 'x' and 'y' = $$\frac{2}{\frac{1}{x} + \frac{1}{y}}$$
Average speed = $$\frac{2}{\frac{1}{70} + \frac{1}{30}}$$
= $$2 \div {\frac{30 + 70}{30 \times 70}} = \frac{2 \times 30 \times 70}{100}$$
= $$2 \times 3 \times 7 = 42$$ km/hr
=> Ans - (A)
Create a FREE account and get:
