Rohan divides his complete journey in three equal parts and covers the first part at a speed of 30 km/h, the second part at 40 km/h and the last part at 50 km/h with his car. What is the average speed (in km/h) of his car during his entire journey?

Correct option is A

Given:
Rohan divides his journey into three equal parts.
Speed during the first part$$(v_1)$$​ = 30 km/h
Speed during the second part$$(v_2)$$​= 40 km/h
Speed during the third part$$(v_3)$$​ = 50 km/h

Formula Used:

​$$\text{Average speed} = \frac{\text{Total distance}}{\text{Total time}}$$​​
Solution:
Let the total Distance be 3D. So, in each part it has to cover Distance = Dkm
​$$\text{Time} = \frac{D}{30} + \frac{D}{40} + \frac{D}{50} = \frac{47D}{600}$$

$$\text{Average speed} = \frac{\text{Total distance}}{\text{Total time}} = \frac{3D}{\frac{47D}{600}} = \frac{1800}{47} = 38 \frac{14}{47} \, \text{km/h}$$​​​