Sachar Louis Sachar 
Sideways Arithmetic from Wayside School [EPUB ebook] 
More than 50 mindboggling maths puzzles! – Rejacketed

Why does elf + elf = fool?How many meals will Miss Mush, the lunch teacher, have to cook for the food to taste as bad as it smells?These Sideways Arithmetic problems may look puzzling at first, but you can use real maths to solve them, and the answers are right there in the book. There are lots of clues and hints; plus all the answers are in the back of the book. Best of all, all the kids you read about in the other books about Wayside School are here to help you!Try solving this, and more than fifty other maths brainteasers, along with the kids from Mrs Jewls’s class. You’ll learn a lot about maths but you’ll be laughing too much to notice!