Talk:Rule of 72
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The compounding table doesn't say how the interest is compounded. Is it continuous? 205.154.230.3 01:16, 19 October 2006 (UTC)
This page does not explain how or why the rule of 72 works. I hear about it, but can not find an explanation of it. Why is the number 72 ? thank you. 208.240.243.170 00:21, 19 May 2007 (UTC)
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- Fintor kindly provided a pointer to the formulae which yield the solution 69.3~. This is pretty close to 72. The reason 72 is used as a close-enough rule-of-thumb most of the time is that it has many small divisors: 1, 2, 3, 4, 6, 8, 9, and 12. When the interest rate you're considering is one of those numbers, one can do the math in one's head. Rule of 70 works well for interest rates of 5%, 7% and 10%. 76.254.85.140 (talk) 19:49, 3 May 2008 (UTC)
