A new medical building containing 100 offices has just been completed. classwife was hired to paint the numbers 1 to 100 on the doors. How many times will she have to paint the number nine? 
Someone please explain the answer of 20...confused
9,19,29,39,49,59,69,79,89,90,91,92,93,94,95,96,97,98,99
The are twenty "9"' on the doors