A bus moving at a speed of 45 km/hr catches a truck 150 metres ahead going in the same direction in 30 seconds. The speed of the truck is

Answer: Option A

Let the speed of truck is = $$x$$ km/h
Their relative speed in same direction = (45 - $$x$$) km/h (Here (45 - $$x$$) has been written because bus crosses the truck which is running 150 meters ahead of it. i.e. Truck speed will be lower than that of bus)
According to the question
$$\begin{array}{rl}& \text{Time}=\frac{\text{Total distance}}{\text{Total speed}}\\ & \frac{150}{\left(45-x\right)\times \frac{5}{18}}=30\\ & \frac{150\times 18}{\left(45-x\right)\times 5}=30\\ & x=27\text{ km/h}\end{array}$$
So, speed of the truck is 27 km/h