UPSC CDS 1 2022 Math Paper

Given:
A car travels from A to B at a speed of 40km∕hr
Travels back from B to A at a speed of 30km∕hr
And again goes from A to B at a speed of 60km∕hr
Formula Used:
Speed = Distance ∕ Time
Average speed = Total distance/Total time
Calculation:
Let the distance between A and B is dkm
According to the question
Total distance =d+d+d=3d
Total time =‌

d

40

+‌

d

30

+‌

d

60

Now, Average speed =‌

3d

d 40 +‌ d 30 +‌ d 60

⇒‌

3d

3d+4d+2d 120

=‌

3d×120

9d

=40km∕hr
∴ The average speed of car in the whole journey is 40km∕hr.