To write all the page numbers of a book, exactly 136 times digit 1 has been used. Find the number of pages in the book.

Explanation:-

From 1- 99 digit 1 is used 20 times. And From 100 - 199, 1 is used 120 times
So, from 1 to 199, 1 is used,
20 + 120 = 140 times
We need 136.So leave 199, 198, 197 and 196
Required pages = 195