A thorough introduction to understanding multiplication and division.

In this follow-up to *Do Not Open This Math Book: Addition + Subtraction* (2018), celebrated mathematician, writer, and actor McKellar returns to guide young readers through multiplication and division via a punny time-machine motif. Comic strips that introduce each section feature McKellar and her two companions (pessimistic Mr. Mouse returns and is joined by peppy Ms. Squirrel) traveling through humorous historical anecdotes that serve as jumping-off points for the math, sometimes in unexpected ways. The organizational flow is intuitive. Charts and visualizations are presented to help readers solve basic problems by understanding number relationships; then memorization tricks are given to help master times tables (some clever, some rhymed); finally, McKellar tackles more complicated concepts (the order of operations, or PEMDAS—with pandas; multidigit problems; and long division). The visuals throughout help in keeping the material so simple that even adults will be able to follow math pedagogy they didn’t learn but that’s currently being used in schools (and there’s a guide in the backmatter). The brilliant-through-simplicity textual explanations are easily accessible to independent readers, and the problem sets (“Game Time” sections in each chapter) are set up for readers to succeed. For extras and more math, McKellar points readers to the book’s website and to her more-advanced middle school book, *Math Doesn’t Suck* (2008).

Multiplies the good times for young mathematicians.

(answer key, index)