June 7, 2013

The Post’s writers may need a course on the meaning of mathematical terms, but they are not guilty of overusing the term “exponential growth.” Letter writer Paul Bennett [“Where X = less than you’d think,” Free for All, May 31] contradicted himself when he suggested that the cost of the U.S. census has not experienced exponential growth but rather can be described as having increased according to “compounded annual growth of about 4.5 percent.” In fact, growth by compounded interest is exponential. There is a reason that exponential growth is a commonly used term.

A huge class of natural phenomena is accurately described by exponential growth and exponential decay, including growth of bacterial colonies, human population growth, bank accounts, decay of radioactive substances, dilution of pollutants, cooling of warm objects, heating of cool objects, responses of living beings to stimuli, genetic complexity, nuclear chain reactions, pyramid schemes, filling and emptying of reservoirs, charge and discharge of capacitors, just to scratch the surface. In fact, it is nearly impossible to overuse the term.

Richard Stone Rothblum, Springfield