RatedrillExact time to double
A time value of money problem from Ratedrill. Solve it with one answer box, with fresh numbers on every attempt and the formula, calculator keystrokes and Excel version in the worked answer, and it is checked the moment you submit.
The task
At 2.5% per year, compounded annually, exactly how many years does it take for money to double? Give the exact answer to 2 decimals, not a rule of thumb.
What this problem teaches
The formula: n = ln(2) / ln(1 + r). The Rule of 72 estimate is 72 / 2.5 = 28.8 years: close, but not exact.
A hint if you get stuck
Doubling means FV / PV = 2, so n = ln(2) / ln(1 + r).
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