Simple interest of an amount for a period of 12 years is Rs.2400. If the amount is tripled after 3 years then what will be the interest after 12 years?

Given:

Simple interest for 12 years = ₹2400

Time (t) = 12 years

After 3 years, amount is tripled

Formula used:

Simple Interest (SI) =

Calculation:

Let the original principal amount be P

SI for 12 years =

⇒ ₹2400 = 

⇒  = 200   ............(1)

SI for first 3 years = 

After 3 years, the principal amount is tripled, so new principal amount = 3P

SI for the remaining 9 years =

Total SI = SI for first 3 years + SI for the remaining 9 years

⇒ SI = +

⇒ SI = +

⇒ SI = +

⇒ SI =

⇒ SI = 30 × 200    (From eqn 1,  = 200 )

⇒ SI = 6000

Therefore, the interest after 12 years is Rs 6000

∴ The correct answer is option (4).