When Numbers Don’t Compute

A professor of computer science at Princeton University, Brian Kernighan has written a new book that features math errors collected from other published works.

Numbers don’t misuse numbers. People do. Just ask Brian W. Kernighan.

A professor of computer science at Princeton University, Kernighan has written a new book called Millions, Billions, Zillions: Defending Yourself in a World of Too Many Numbers (Princeton University Press). The book features math errors Kernighan collected from other published works. One common error he notes is confusing millions and billions and percentage and percentage points.

One of the whoppers he found came from Staying Safe at School, a 2011 book by Chester and Tammy Quarles. The authors wrote: “Every year since 1950, the number of American children killed with guns has doubled.”

“That statement doesn’t stand up to much scrutiny,” says Kernighan, 76. “Suppose a single child was killed by gunfire in 1950. Then there would be two in 1951, four in 1952, over a thousand by 1960, over a million by 1970, a billion by 1980 and a trillion by 1990,” he writes.

The book offers suggestions on how to recognize invalid claims using sixth-grade arithmetic, such as reasoning backward from a conclusion. For example, in 2004, a New Jersey newspaper reported: “Shutting down your computer and monitor overnight rather than running them 24 hours a day will save $88 a day.”

If true, that would mean an unlikely savings of more than $30,000 a year, Kernighan notes. The paper ran a correction acknowledging that the actual savings would be $88 a year.

“The problem with math is it’s poorly taught,” says the Princeton resident, “but I think people can get better at it.”

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