Question

A car travelled at a speed of 60 km/h for 2 h between cities A and B, and 90 km/h for the next 3 h between cities B and C. What is the average speed of the car between cities A and C?​

• A.
  75 km/h
• B.
  55 km/h​
• C.
  78 km/h
• D.
  60 km/h

Answer 1

The correct option is C

78 km/h
We know that,
$Averagespeed=\frac{Totaldis\tan cetravelled}{Totaltimetaken}$
Average speed between cities A and C = (Distance travelled by car between cities A and C)/ (Time taken to reach city C from city A)

Distance travelled between cities A and C = Distance between A and B + Distance between B and C.

We know that Distance = speed * time
Distance between cities A and B = 60 km/h * 2 h = 120 km
Distance between cities B and C = 90 km/h * 3 h = 270 km

Total time taken from city A to C = 2 h + 3 h = 5 h

Thus, the Average speed between cities A and C = (120 +270)km /5 h
= 390/5
= 78 km/h