Question 9
The Funny Book has its pages numbered in the following way: 1, 2, 2, 3, 3, 3, 4, 4, 4, 4, 5, ... . That is, there is one 1, two 2s, three 3s, four 4s, five 5s, and so on. How many actual pages (including front and back) will the Funny Book have if it contains all possible pages that are numbered “1” through “20,” but not any that are numbered “21”?