The driver of an ambulance sees a school bus 40 m ahead of him after 20 seconds, the school bus is 60 meter behind. If the speed of the ambulance is 30 km/h, what is the speed of the school bus?

Explanation:-

Relative Speed,
= ^{(Total distance)}/_{(Total time)}
= ^{(60 + 40)}/₂₀
= 5 m/s = ^{(5 * 18)}/₅ = 18 kmph
Relative Speed = (speed of ambulance - speed of school bus)
Speed of school bus = speed of ambulance - relative speed.
= 30-18 = 12 kmph.