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Rule of 72: What it is and how to use it

Here’s how the Rule of 72 works: Divide 72 by your expected annual interest rate (as a percentage, not a decimal). The answer is roughly the number of years it will take for your money to double. For ...
Nature

Quick and Easy Methods of Calculating A Simple Explanation of the Theory and Use of the Slide-Rule, Logarithms, &c

THE author makes his title, “Quick and Easy Methods of Calculating”—at least, that is all that is in large print on the title-page; but the binder calls it, on the outside of the book, “The Slide-Rule ...