Drivers are concerned with the mileage obtained by their automobiles. One driver has kept track of several tankfuls of gasoline by recording miles driven and gallons used for each tankful. Develop a sentinel-controlled-repetition script that prompts the user to input the miles driven and gallons used for each tankful. The script should calculate and display the miles per gallon obtained for each tankful. After processing all input information, the script should calculate and display the combined miles per gallon obtained for all tankfuls (that is, total miles driven divided by total gallons used). Enter the gallons used (-1 to end): 128
Enter the miles driven: 287 The miles/gallon for this tank was 22.421875
Enter the gallons used (-1 to end): 10.3
Enter the miles driven: 200 The miles/gallon for this tank was 19.417475
Enter the gallons used (-1 to end): 5
Enter the miles driven: 120 The miles/gallon for this tank was 24.000000
Enter the gallons used (-1 to end): -1 The overall average miles/gallon was 21. 601423

In Python:

gals= float(input("Enter the gallons used (-1 to end): "))

miles = float(input("Enter the miles driven: "))

mileage = 0.0

count = 0

while not (gals == -1):

   count += 1

   mileage +=(miles/gals)

   print("The miles/gallon for this tank was "+str(round(miles/gals,6)))

   gals= float(input("Enter the gallons used (-1 to end): "))

   miles = float(input("Enter the miles driven: "))

print("The overall average miles/gallon was "+str(round(mileage/count,6)))

Explanation:

#This prompts the user for the number of gallons used

gals= float(input("Enter the gallons used (-1 to end): "))

#This prompts the user for miles driven

miles = float(input("Miles driven: "))

#This initializes the mileage to 0

mileage = 0.0

#This initializes the count of vehicles to 0

count = 0

#The following is repeated until input for gallons is -1

while not (gals == -1):

#The count of vehicles is increased by 1

   count += 1

#The total mileage for all cars is calculated

   mileage +=(miles/gals)

#This prints the mileage for that particular vehicle

   print("The miles/gallon for this tank was "+str(round(miles/gals,6)))

#This prompts the user for the number of gallons used

   gals= float(input("Enter the gallons used (-1 to end): "))

#This prompts the user for miles driven

   miles = float(input("Miles driven: "))

#This calculates and prints the overall average mileage  

print("The overall average miles/gallon was "+str(round(mileage/count,6)))