A pictograph of books read uses one symbol to stand for 8 books, and part-symbols are allowed. Aarav 4.5 symbols, Bela 3 symbols, Chetan 5.25 symbols. How many more books did Chetan read than Bela?

Chetan's 5.25 symbols stand for $5.25\times 8=42$ books and Bela's 3 symbols for $3\times 8=24$ books, a difference of 42 − 24 = 18 books. Reading off the difference in symbols alone gives 2.25 and forgets that one symbol is worth 8 books, while 24 is Bela's own total.