What is the minimum number of full years required for an investment to more than double at a compound interest rate of 20% per annum?

Explanation

Let the principal be P. After n years at 20% compound interest, the amount is P(1 + 0.20)^n = P(6/5)^n. We want the amount to exceed 2P, so (6/5)^n > 2. Calculating powers, (6/5)^4 = 1.296 * 1.296 ≈ 2.07 > 2, so the smallest integer n satisfying this is 4 years.