Answer:
80 mph
Explanation:
Her drive from City A to City B is 240 miles. She drives at an average speed of 60 mph.
s = d/t
t = d/s
t = 240 miles / 60 mph = 4 hours
The trip should take a total of 4 hours by going directly from City A to City B at an average speed of 60 mph and making no stops.
She drives 120 miles and stops for 30 minutes.
She drives 120 miles from City A to the landmark at the average speed of 60 mph.
s = d/t
t = d/s
t = 120 miles / 60 mph = 2 hours
It takes her 2 hours to get to the landmark.
Now she stops for 30 minutes = 0.5 hour
She now needs to drive another 120 miles and still only take 4 hours total time.
She drove 2 hours to the landmark. She stopped for 0.5 hours.
Total time so far: 2.5 hours
The total trip should take 4 hours to keep her overall 60 mph average speed.
Time left to drive: 4 hours - 2.5 hours = 1.5 hours
Distance left to drive: 120 miles
s = d/t
s = 120 miles / 1.5 hours
s = 80 mph
She must drive from the landmark to City B at an average speed of 80 mph.
Answer: 80 mph