Compound interest on a certain sum at the rate of 10% per annum after 2 years is Tk. 4410. Find the simple interest on that sum at the rate of 12% per annum for 5 years.

Question: Compound interest on a certain sum at the rate of 10% per annum after 2 years is Tk. 4410. Find the simple interest on that sum at the rate of 12% per annum for 5 years.

Solution:
Let the sum be, x.
Rate of interest = 10%
Period = 2 years

Hence, compound interest = x(1 + 10/100)² - x = 4410
⇒ x × 1.21 - x = 4410
⇒ 0.21x = 4410
⇒ x = 4410/0.21
∴ x = 21000

Hence, simple interest = 21000 × (12/100) × 5
= 12600