There are two books sitting side by side, consisting of exactly 100 pages. The book on the left is upside down. If you add the page number at the extreme left side of the book on the left to the page number at the extreme right side of the right hand book, what is the total?
The total is 2.
When the book on the left is upside down then the page number on the extreme left is 1 and the right hand side book’s extreme right hand side page number is also 1.
Another way to look at the problem: If two books are standing side by side to each other, page 1 is on the right side of each book (assuming you are looking at the spine of the books). Turning the one on the left upside down (with the book spine still pointing out), brings page 1 to the left side. And so at the “extreme left” of the book on the left is page 1, while the “extreme right” of the book on the right is also page 1.