Final answer:
To find the total average speed, add the speeds of the different parts of the trip and divide by the total time.
Step-by-step explanation:
To find the total average speed, we need to calculate the total distance traveled and the total time taken.
Oliver drove the first 90 miles in 1.5 hours, so his speed for the first part of the journey was 90 miles / 1.5 hours = 60 miles per hour.
For the remaining 120 miles, Oliver took 3 hours, so his speed for the second part of the journey was 120 miles / 3 hours = 40 miles per hour.
To find the total average speed, we can use the formula:
Average speed = Total distance / Total time
For Oliver's journey, the total distance is 90 miles + 120 miles = 210 miles, and the total time is 1.5 hours + 3 hours = 4.5 hours.
Therefore, the total average speed is 210 miles / 4.5 hours = 46.67 miles per hour.