SOLUTION: A rule of thumb for finding how long it takes an investment to double is called the rule of seventy. To apply the rule, divide 70 by the interest rate written as a percent. At 5% a
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Question 312862: A rule of thumb for finding how long it takes an investment to double is called the rule of seventy. To apply the rule, divide 70 by the interest rate written as a percent. At 5% an investment takes 70/5 = 14 years to double. At 7%, it takes 70/7=10 years. Explain why this formula works.
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