Apple’s New Math. Or: Why a $15 E-Book Equals a $75 Paper Book.

McGraw-Hill normally sells high school textbooks for $75 a pop. Now it says it will sell electronic versions of the same books, via Apple, for $15 apiece. How can the publisher make that work?

“Volume,” says McGraw-Hill CEO Terry McGraw, which is the usual answer for this kind of digital question. But there’s an important asterisk here, too. Normally, McGraw-Hill would sell its books directly to public schools, which would keep the texts for an average of five years.

Under Apple’s new textbooks plan, though, McGraw-Hill will try something different: It will sell its books directly to each student (the student could either pay out of pocket, or the school could fund the purchase via a voucher/code), who will use the book for a year, then move on. They’ll be able to keep the digital text, but won’t be able to resell it or pass it along to another student, and McGraw-Hill anticipates that another set of students will buy new books the following year.

So Terry McGraw figures that over five years he’ll generate the same total sales selling $15 e-books as he would selling $75 books. It’s not a total push, because in this model, Apple will take an undisclosed cut of sales — McGraw-Hill execs wouldn’t go into details, so let’s assume for now that it’s Apple’s standard 30 percent — but presumably McGraw-Hill can make some of that up by forgoing the costs of print and distribution.

(It’s important to note that all of this is about the high school textbook market, for now. While McGraw-Hill and other publishers sell college texts through other digital platforms, they still haven’t announced plans to do so with Apple.)

All of that assumes that the book pricing stays at $15. After Apple’s event, McGraw-Hill executives repeatedly used the phrase “pilot pricing” to describe their near-term plans. And they told me that they have the ability to change the price when and if they want.

But when I posed the same question to Apple media boss Eddy Cue just now, I got a much different response. “This isn’t pilot pricing,” he said. “All of our books will be $14.99.”