Charles E. Hill 
This picture book tells how two young children, X and Y, work with their Aunt Z to bake an infinite pie.
Aunt Z helps them discover how to use “flour, butter and water” to bake endless ways to create pies. X turns the dough into circles while Y turns the dough into a triangle. They fill their pies with strawberries, chocolate and banana. Some of the pies have four sides, while others have eight.
The book is best for fourth grade and up. Concepts like infinity are more advanced and difficult for young students to understand. For example, X says, “My round cake has infinite corners!” This is a complex and abstract idea to visualize for young learners. And as Y says, “But… there seems to be no corners.” Most students will need a teacher or parent to explain how a circle can be made up of infinite corners.
A teacher could use this text as an opportunity for older students to identify mathematical concepts like fractals and exponentials. The author uses triangles to create a clay Koch snowflake. She also shows exponentials by asking the bakers to fold the puff pastry repeatedly.
It’s a fun book and the bright colors and pictures that illustrator Ren drew of Aunt Z, X and Y are nice. The Asians in the book look like people we might know. They are not stereotyped. Use this book to introduce readers to complex ideas such as infinite corners, X and Y axes, different geometric shapes, and infinity.
A short interview with the author and mathematician of the book, Eugenia Cheng
IE: What grades is Bake Infinite Pie with X+Y intended for?
Eugenie Cheng: Bake an infinite pie with X+Y is listed for ages 4-8, but I can see why that might come as a surprise. Math concepts may seem quite advanced, but ideas are things that can spark the curiosity and imagination of little children of all ages.
It would take advanced math to make these ideas precise and fully explain the math behind them, but I love talking about the ideas with kids without having to go into the full math explanations. I think too often we think we’re supposed to understand all the calculations we see, but in fact no one really understands these things. I think it’s more important to think about it and let the children’s minds wonder and wonder, rather than trying to get them to understand everything.
Imagine if it were a book about the weather. It might introduce kids to rain, snow, thunder, lightning, hurricanes, and tornadoes, but we wouldn’t expect them to understand all of the meteorology that causes these phenomena.
IE: How can teachers explain complex concepts like infinity?
EC: For children of this age, I don’t think the concepts need to be explained, rather explored. We can get little kids thinking about ideas and then exploring them, just as we explore music and art rather than explain them. We can get them to think of infinity as something so big that it lasts forever.
IE: How can parents teach the concepts of infinity, fractals and exponentials to their young children?
EC: I’ve spoken to many parents who are afraid to talk about math with their children because they feel like they don’t understand it themselves. I would just ask them to talk about it anyway! Parents can explore the ideas with their children and if the children ask them questions they don’t know how to answer, that’s fine, and they could discuss how to investigate together. The internet has many helpful explanations of math concepts, and I believe in celebrating children when they ask a math question that an adult can’t answer.
