Final answer:
The car's average speed for the whole journey is calculated by adding the total distance traveled during each leg and dividing it by the total time taken, resulting in an average speed of 54 mph.
Step-by-step explanation:
To calculate the average speed of the car for the whole journey, we must first find the total distance traveled and then divide it by the total time taken. This involves converting minutes into hours to maintain consistent units.
- First leg: 15 minutes is 0.25 hours. At 48 mph, the distance = speed × time = 48 mph × 0.25 h = 12 miles.
- Second leg: 2 hours at 60 mph. The distance = 60 mph × 2 h = 120 miles.
- Third leg: 45 minutes is 0.75 hours. At 40 mph, the distance = 40 mph × 0.75 h = 30 miles.
The total distance is 12 miles + 120 miles + 30 miles = 162 miles. The total time is 0.25 h + 2 h + 0.75 h = 3 hours.
Now we find the average speed using the formula: average speed = total distance / total time. So, the car's average speed = 162 miles / 3 h = 54 mph.