Author and Editorialist : Dhruv Mahajan
Average Speed is Not (u+v)/2.
But it is (total distance covered)/(total time taken).
Let distance from A to B is ‘d’, then time taken from A to B is d/u.
And distance between B to A will also remain ‘d’, hence time taken from B to A is d/v.
Total distance covered in the journey is 2d.
Hence average speed will be (total distance covered)/(total time taken),
which is (2d)/(d/u+d/v) which is equal to 2uv/(u+v).
Remember if u=0 and v=0 then avg speed will also be zero.