Here is my code. I need to add a percent symbol at the end of the print string. I can't get this figured out. 
total = 0
counter = 0
while True:
    score = int(input('Enter test score: '))
    if score == 0:
        break
    total += score
    counter += 1
average = total / counter
print('The average is:', format(average, ',.3f'))
 
     
     
    