Let’s denote the principal amount as P.

Compound Interest (CI) formula:

CI = P × (1 + R/100)^Time – P

Given values:

R = 20% per annum

We want to find the least number of complete years (Time) for which the amount will be more than doubled, i.e., Amount > 2P.

Amount = P × (1 + 20/100)^Time

= P × (1.2)^Time

We want to find the Time for which:

P × (1.2)^Time > 2P

Divide both sides by P:

(1.2)^Time > 2

Take the logarithm (base 10) of both sides:

Time × log(1.2) > log(2)

Time > log(2) / log(1.2)

Time > 3.802

Since Time must be a whole number (complete years), the least number of complete years is:

Time = 4

The least number of complete years is 4.