Newspaper Puzzle

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 you 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.
Then you had to notice that the numbers were arranged in pairs, with the first pair adding up to 64 and the second pair adding up to 66.
64-45 = 19
66-46 = 20
So the four pages on this sheet are 19, 20, 45 and 46.