Excluding stoppages, the speed of a bus is 54 kmph, and including stoppages, it is 45 kmph. For how many minutes does the bus stop per hour?

The bus stops for 10 minutes per hour.

Without stops it does 54 km, with stops only 45 km in an hour.

Lost distance = 54 - 45 = 9 km.

Time to cover 9 km at 54 kmph is the stoppage time.

Stoppage = (9 / 54) x 60 = 10 minutes.

So the bus stops 10 minutes per hour.