Question

Arnab deposited a sum of Rs. 12000 at compound interest becomes triple after 5 years. After 20 years it will be, 
1. 972000
2. 900000
3. 987000
4. 872000

Answer 1

Correct Answer - Option 1 : 972000

Given 

Principal = Rs 12000 

Concept Used 

In compound interest, the principal is increased by the time in powers 

Amount = P (1 + R/100)^t

Calculation 

Let the principal be x 

After 5 years, 

Amount = 3x 

⇒ 5 × 4 = 20 years 

so, amount will become = (3)⁴x = 81x

⇒ x = Rs 12000

⇒ 81x = 81 × 12000 = 972000

∴ The amount will become after 20 years is Rs 972000