At OIT’s **Lunch ‘n Learn** seminar on Wednesday February 22, Computer Science Professor Brian Kernighan presented ** Millions, Billions, Zillions – Why (In)numeracy Matters**. In 2004, Newsweek magazine stated: “Perhaps the Bush administration could use the 660-billion-barrel Strategic Petroleum Reserve to push prices down. Given that the average vehicle uses 550 gallons a year, assuming that there are 300 million cars and that a barrel contains approximately 50 gallons, our yearly oil needs work out to about 3 billion barrels a year. And so, offered Dr. Kernighan, “Why are we so worried about oil?”

The answer is, of course, that our Strategic Petroleum Reserve is actually 550 million barrels, enough for 200 days, not 200 years.

Why does innumeracy matter? In an example, from the Newark Star Ledgar, a man accepted an alimony agreement that would pay his wife $250 a month until she remarried, with payments to increase by 5% a year. The rule of 72 permits us to divide 72 by the rate to find the number of periods. In this instance, 72/5 tells us that payments would double every 14 years. He apparently failed to predict that his still unmarried wife, 32 years later, would now be getting $1,200 monthly.

There were examples that required no complex explanations. Noting the disappearance of glaciers at the rate of 1% a year, a climate web site predicted that glaciers would be gone in 100 years. Dear Abby reported that Americans receive almost 2 tons of junk mail every day, which works out to 13 pounds per person per day.

Dr. Kernighan offered some common sense principles for estimating when presented with inaccurate or incomplete or uncertain information. Does the number make sense? Does it agree with, or run counter to, your experience? What would be the implications if the number were accurate? For example, the Star Ledgar reported in 1992 that the Passaic River was flowing at about 200 miles an hour. The London Times reported that a NASA jet traveled 850 miles in 10 seconds.

Some of the errors appear to be introduced by conversions to and from metric. Such conversions, for example, can introduce more significant digits than may be justified: “Drug sniffing dogs found a cache of 22 pounds of heroin.”

And so, says Dr. Kernighan, recognize the enemy, from bad estimates and excessive precision through arithmetic errors and suspect motives. Learn useful numbers and facts, including basic populations, rates, sizes, and areas. Learn basic arithmetic shortcuts like the Rule of 72 and that 2^{10} is approximately 10^{3}.

Above all, use your common sense and experience. Does it make sense, and how could they know?

Links to Dr. Kernighan’s presentation are available on the Lunch ‘n Learn web site.