Math Riddle: A new medical building containing 100 offices had just been completed. Mark was hired to paint the numbers 1 to 100 on the doors. How many times will Mark have to paint the number nine?
Answer: The correct answer is 20! 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99.