Weegy: 36 years to double. use the rules of 72. Let R * T = 72, where R = the rate of growth (for example, interest rate), T = doubling time (for example, time it takes to double an amount of money). Plug in the value for R = rate of growth. [ For example, how long does it take to double $100 to $200 at an interest rate of 2% per annum? Substituting R = 2, we get 2 * T = 72. = 36 years. ] (More)

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