A sum of money doubles itself in 6 years at compound interest. In how many years will it become 4 times itself?

💡 Solution & Explanation

With compound interest the sum keeps doubling every 6 years: 2 times after 6 years, 4 times after 12, 8 times after 18, and so on. 4 = 2^2, so it takes 2 doublings: 2 × 6 = 12 years. Multiplying 6 by 4 (24 years) would be the simple-interest way of thinking, which does not apply here.