Anil completed a certain journey by a car. If he covered 35% of the distance at 70 km/h. 40% of the distance at 80 km/h and the remaining distance at 50 km/h, his average speed (in km/h) for the entire journey is:

Correct option is B

Given:

Anil covered 35% of the distance at a speed of 70 km/h.
He covered 40% of the distance at a speed of 80 km/h.
He covered the remaining 25% of the distance at a speed of 50 km/h.

Formula Used:

The average speed for the entire journey is given by:
​$$\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time}}$$​​

Solution:

Let Anil cover a total distance =  100 km

Time taken by Anil to cover 35 km:
​$$\frac{35}{70} = \frac{1}{2} \ \text{h}$$​​
Time taken by Anil to cover the next 40 km:
​$$\frac{40}{80} = \frac{1}{2} \ \text{h}$$​​

Time taken by Anil to cover the remaining 25 km:
​$$\frac{25}{50} = \frac{1}{2} \ \text{h}$$​​

Average speed:
​$$\text{Average Speed} = \frac{\text{Total Distance}}{\text{Total Time Taken}}\\\ \\= \frac{100}{0.5 + 0.5 + 0.5} = \frac{100}{1.5} = \frac{1000}{15} = 66\frac{2}{3} \ \text{km/h}$$​​