An airplane flies 40km directly south in 10 minutes and 20 km directly east in five minutes, its average speed is:

a) 2.98km/min

b) 2km/min

c) 8km/min

d) 4km/min

Average speed = total distance / total time

total distance = 40 + 20 = 60km

total time taken = 10 + 5 = 15 minutes

Average speed = 60/15 = 4km/min

D. 4km/min

Explanation:

Since the question deals with "speed" and not "velocity", the direction does not matter.

the plane covers 40 + 20 km=60km in 10mins + 5 mins=15mins

60 km - 15 mins

1min - 60:15 = 4 mins

therefore, your answer is D. 4km/min