A newspaper made of 16 large sheets of paper folded in half. The newspaper has 64 pages altogether. The first sheet contains pages 1, 2, 63, 64.
If we pick up a sheet containing page number 45. What are the other pages that this sheet contains?
On the back of 45, it is 46. The pages are such that for each page p, 65-p will be also on the same page.
65–45 = 20
65–46 = 19
So the four pages in this sheet are 19, 20, 45, 46.