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How long to double · Part 3 of 3
An investment compounds once a year at a fixed rate. You are asked a sequence of growth questions, each a step further from the rule of thumb.
Using the rule of 72, what annual rate, in per cent, makes money quadruple in 12 years?
Answer with a number. Fractions, powers and expressions like 23/6 or C(52,5) are read correctly in practice.
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