Final answer:
Marty's average speed for the entire bike trip is 12.8 miles per hour, calculated by dividing the total distance of 16 miles by the total time of 1.25 hours.
Step-by-step explanation:
Marty went on a bike ride to the store that was 8 miles away. It took him 3/4 of an hour to get there and 1/2 of an hour to get back. To calculate the average speed for the entire trip, we must first determine the total distance traveled and the total time taken.
Since Marty traveled 8 miles to the store and 8 miles back, the total distance is 16 miles. The total time taken is 3/4 hour (to get there) + 1/2 hour (to get back), which is 5/4 hours or 1.25 hours in decimal form. The formula for average speed is Total Distance / Total Time.
Therefore, Marty's average speed for the trip is 16 miles / 1.25 hours = 12.8 miles per hour.