Correct Answer - Option 3 : 16 years
Given:
A sum of money placed at compound interest doubles itself in 8 years.
Formula used:
A = P(1 + R/100)n
where A = amount
p = principal
R = rate
n = time
Calculations:
Let P be Rs.1, then A = Rs.2
A = P(1 + R/100)n
⇒ 2 = 1(1 + R/100)8
⇒ 4 = 1(1 + R/100)16 (by squaring both sides)
comparing this to A = P(1 + R/100)n
we get n = 16 years
∴ the correct answer is 16 years.