You would think a book of 48 pages would always have the same number of pages, wouldn't you? But you'd be wrong...
Books always have multiples of eight pages, because of the way paper is folded to make a book. So short books for short children generally have 24, 32, 48, 56 or 64 pages. A lot of schools and libraries books have 48 pages. It's long enough to get some decent content in, but short enough to be unintimidating to novice readers.
Traditionally, the main text of a 48-page book starts on page 4 and continues until page 45. The prelims come before page 4, and the end matter (glossary, further info, index) comes on pages 46 to 48. But 48-page books have got shorter. More and more often, they are self-ended. This means the first and last pages are stuck down, becoming the endpapers. The main text then starts on page 6 and ends on page 43. The reasons are economic. The publisher can pay you less to write it (typically £100 less), they have to pay less for layout, editing, proof-reading and licences for pictures from picture libraries. It costs less to print and bind. But the cover price remains the same.
It is, literally, money for nothing (on those stuck down pages) for the publisher.