Question : A car travels a certain distance at 70 km/hr and comes back at 30 km/hr. Find the average speed for the total journey.
Option 1: 42 km/hr
Option 2: 50 km/hr
Option 3: 34 km/hr
Option 4: 58 km/hr
Correct Answer: 42 km/hr
Solution :
Given:
The car goes at speed($S_1$) = 70 km/hr
The car returns at speed($S_2$) = 30 km/hr
Average speed = $\frac{2×S_1×S_2}{S_1+S_2}$ (for the same distance at different speeds)
= $\frac{2×70×30}{70+30}$
= $\frac{4200}{100}$
= 42 km/hr
Hence, the correct answer is 42 km/hr.
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