Madhya Pradesh Police Exam Model Paper 8

Given:
The ratio of the speed of the bike, van and lorry = 3 ∶ 7 ∶ 5
Distance covers by lorry = 360 km
Time taken by lorry to cover = 12 hours
Concept used:
Speed = Distance/Time
Average = (Total sum)/(Total terms)
Calculations:
Let the speed of the bike, van and lorry be 3x, 7x and 5x respectively
Speed of lorry = 360/12 = 30 km/h
$\Rightarrow 5\mathit{x}=30$
$\Rightarrow \mathit{x}=6$
Speed of bike $=3\mathit{x}=3\times 6=18$
Speed of van $=7\mathit{x}=7\times 6=42$
Average speed of bike and van $=\left(18+42\right)/2=30$ km/h
∴ Average speed of bike and van is 30 km/h