Madhya Pradesh Police Exam Model Paper 9

Given:
Speed while going = 40 km/hr
Decrease in speed while returning = 20%
Formula used:
Average speed when distance covered is same = $2\mathit{x}\mathit{y}/\left(\mathit{x}+\mathit{y}\right)$
Where, x = Speed while going
y = Speed while returning
Calculation:
Speed while returning $=40\times [\left(100\mathit{–}20\right)$/$100]$ km/hr
$\Rightarrow 40\times \left(80/100\right)$ km/hr
⇒ 32 km/hr
Now, average speed $=\left(2\times 40\times 32\right)/\left(40+32\right)$ km/hr
$\Rightarrow \left(80\times 32\right)/72$ km/hr
⇒ 35.56 km/hr
∴ The average speed of the whole journey is 35.56 km/hr