TIFR CSE 2020 | Part A | Question: 9

Question

A contiguous part, i.e., a set of adjacent sheets, is missing from Tharoor’s GRE preparation book. The number on the first missing page is $183$, and it is known that the number on the last missing page has the same three digits, but in a different order. Note that every sheet has two pages, one at the front and one at the back. How many pages are missing from Tharoor's book?

• A. $45$
• B. $135$
• C. $136$
• D. $198$
• E. $450$

Answer 1

The last missing page number is $318$.Hence number of pages missing is given by $318-183{\color{red}{+1}}=136$.

Few more points:

• Since each sheet has page numbers on front and back.Hence if we start numbering the pages from $1$(front) and $2$(back) of the $1^{st}$ sheet, then odd page numbers will be on front of every sheet and even page number in the back.As given last page of the missing sheet,hence it should be even page number($8$ as last digit)
• The ${\color{red}{+1}}$ for counting the number of pages(as shown above) is for counting page no. 183 as well. 

Answer 2

number of numbers between two numbers [a,b] i.e b-a +1

hence

318-183+1 = 136 pages were missing