Question

A motor starts with the speed of 70 km/hr with its speed increasing every two hours by 10 km/hr. In how many hours will it cover 345 km?

• A. $2\frac{1}{4}$ h
• B. $4\frac{1}{2}$ h
• C. $4h5min$
• D. Cannot be determined

Answer 1

The correct option is B $4\frac{1}{2}$ h

Distance covered in first 2 hours $=(70$x$2)km=140$ $km$
Distance covered in next 2 hours $=(80$x$2)km=160$ $km$
Remaining distance $=345-(140+160)=45km.$
Speed in the fifth hour $=90$ $km/hr$
As speed is $90$ $km/hr$ means it covers $90$ $km$ in $1hr$
So, if it covers $90$ $km$ in $1hr$, then
$45$ $km$ is covered in $\frac{45}{90}=\frac{1}{2}hr$
Total time taken $=2+2+\frac{1}{2}=4\frac{1}{2}hr$