The diagram below shows the method of construction of a book with four folded sheets in each

Question

block, and three blocks in total. Page one is the first page of the first block of four sheets. At the
centre of each block, you can see the stitching that binds the book together.

A book is to be made using the same technique but with eight sheets of paper in each of the
three blocks.
Which of the following pairs of pages could be in the centre of a block (that is, if opened there,
the stitching would be visible)?

I don't really get why the answer's 48 and 49 here. And what is this type of problem called? I never get the gist of it.

Answer 1

There are 24 sheets of paper. Once they are stacked up, page 1 will be on the bottom left, and 24 sheets later, on top (the middle of the book when folded) there will be page 24 on the left (2 pages per sheet), and 49 on the right.