Answer:
Average speed of the trip = 52.9 km/h
Distance between initial pairs of cities (start to end) = 70.0 km
Explanation:
Since distance = speed × time
If she drives 30.0 min at 80.0 km/h
Distance covered = (30/60) × 80 = 40.0 km
Again she drives 45.0 min at 40 km/h
Distance covered = (45/60) × 40 = 30.0 km
Again she drives 12.0 min at 100 km/h
Distance covered = (12/60) × 100 = 20.0 km
Total distance covered = 40.0 + 30.0 + 20.0
= 90.0 km
Total time spent = 30.0 + 45.0 + 12.0 +15.0
= 102 min
Average speed for the trip = Total distance covered/total time spent
= 90/(102/60)
= 52.9 km/h
Distance between initial cities will be between the start of one city to the end of another
Between the first pairs = 40.0 + 30.0 = 70.0 km
Between the second pairs = 30.0 + 20.0 = 50.0 km
