Madhya Pradesh Police Exam Model Paper 4

Given:
A person goes from a place to another place with the speed = 30 km/hr
The person returns to his place with the speed = 50 km/hr
Formula:
If in these types of questions, the distance is same then
Average Speed $=\left(2\times \mathit{S}1\times \mathit{S}2\right)/\left(\mathit{S}1+\mathit{S}2\right)$
Where, S1 is the speed from A to B and S2 is the speed from B to A
Calculation:
Average speed $=\left(2\times \mathit{S}1\times \mathit{S}2\right)/\left(\mathit{S}1+\mathit{S}2\right)$
$=\left(2\times 30\times 50\right)/30+50$
= 37.5 km/hr