Question

From 09:00 pm to 10:00 pm, a person drove at a speed of 40 km/h, then he took a halt for an hour. He resumed his journey at 11:00 pm and drove till 12:00 am midnight at a speed of 50 km/h. What is his average speed in the time interval between 09:00 pm and 12:00 am?

• A. 90 km/h
• B. 40 km/h
• C. 30 km/h
• D. 45 km/h

Answer 1

The correct option is C 30 km/h

We know that,
Speed = $\frac{Distance}{time}$
$\Rightarrow$Distance = Speed $\times$ time

Between 9:00 pm and 10:00 pm,
Distance travelled = 40 km/h $\times$ 1 h
= 40 km

Between 10:00 pm and 11:00 pm, the person doesn’t travel.
So, the distance travelled = 0

Between 11:00 pm and 12:00 am,
Distance travelled = 50 km/h $\times$ 1 h
= 50 km

For the whole journey,
Average speed = $\frac{Totaldistance}{Totaltime}$
= $\frac{(40+0+50)km}{(1+1+1)h}=\frac{90}{3}$km/h = 30 km/h