Digit 1 is occurring 136 times on writing all of the page numbers of a book. What will be the number of pages in the book?

Question: Digit 1 is occurring 136 times on writing all of the page numbers of a book. What will be the number of pages in the book?

Solution:
From 1 - 99, the digit 1 occurs 20 times,
from 100 - 199, the digit 1 occurs 120 times.
So, from 1 to 199, the digit 1 occurs 20 + 120 = 140 times
According to question 1 is occurring only 136 times, which means we need to remove 196, 197, 198, and 199.
So, the required number of pages will be 195.