Rule of 72 is a method for estimating the time required for a given principal to double. It is calculated as t = ln 2 / (ln(1+r)) and can be approximated as \(t \approx 0.72/r\). It is especially used in finance to estimate an investment's doubling time. For example, when the rate is 6%, 0.72/0.06 = 72/6 = 12 years is required to double the investiment, where the actual value is about 11.896.
In Greek-based number-naming systems, 72 is associated with prefix "duheptaconta-", and with prefix "duoseptuaginti-" in Latin systems.
It is also the number of possible pawn moves (by a given player) in shogi.
In TV broadcasting
In the Americas, the mid gap in the Band I starts at 72 MHz.
- MathWorld, Rule of 72