After 3 years a principal amount becomes Rs. 3600 and after 6 years the amount obtained is Rs. 4800 both at same rate of compound interest. What is the principal amount?

1. Rs. 3300

2. Rs. 2100

3. Rs. 3600

4. Rs. 2700

1. Rs. 3300

2. Rs. 2100

3. Rs. 3600

4. Rs. 2700

Correct Answer – Option 4 : Rs. 2700

Given:A

_{1}= Rs. 3600, N_{1}= 3 yearsA

_{2}= Rs. 4800, N_{2}= 6 yearsFormula used:A = P × {1 + (R/ 100)}

^{N}Where P = Principal amount, R = Rate of interest in %, N = Number of years

Calculation:Assuming Rate of compound interest = R% and principal amount = Rs. X

Now, according to equation

⇒ 3600 = X × {1 + (R / 100)}

^{3}—-(1)⇒ 4800 = X × (1 + (R / 100))

^{ 6}—-(2)Dividing Equation 2 by Equation 1

⇒ 4800/3600 = {1 + (R / 100)}

^{3}⇒ 4 / 3 = {1 + (R / 100)}

^{3}—-(3)Substituting Equation (3) in Equation (1)

⇒ 3600 = X × (4 / 3)

⇒ 3600 × (3 / 4) = X

⇒ 2700 = X

∴ Principal amount is Rs.. 2700.