Suman invested a sum Rs.20,000 at 10% per annum compound interest. If she received an amount of Rs.26,620 after n years, the value of n is:

Correct option is C

Given:

Principal (P) = Rs. 20,000

Rate of Interest (R) = 10% per annum

Amount (A) = Rs. 26,620

Time (n) = ?

Concept Used: 

Compounded Amount ;

A = P $$\left(1 + \frac{R}{100} \right)^n$$​

Solution: 

Now, applying the formula;

26620 = 20000 $$\left(1 + \frac{10}{100} \right)^n$$​

$$26620 = 20000 \left(\frac{110}{100}\right)^n\\ \ \\\frac{26620}{20000} = (\frac{110}{100})^n\\ \ \\\frac{1331}{1000} = \left(\frac{110}{100}\right)^n\\ \ \\\left(\frac{11}{10}\right)^3= \left(\frac{11}{10}\right)^n$$​

n = 3 Years 

Alternate Method: 

So in 3 years the amount became ₹26,620