The compound interest on a certain sum for 2 years at 10% per annum is Tk. 525. The simple interest on the same sum for double the time at half the rate percent per annum is:

Question: The compound interest on a certain sum for 2 years at 10% per annum is Tk. 525. The simple interest on the same sum for double the time at half the rate percent per annum is:

Solution:
Let the sum be Tk. P.

ATQ,
P {1 + (10/100)}² - p = 525
⇒ P[{1 + (1/10)}² - 1] = 525
⇒ P{(11/10)² - 1} = 525
⇒ P{(121/100) - 1} = 525
⇒ P(21/100) = 525
⇒ P = (525 × 100)/21
∴ P = 2500

We know,
Simple interest, I = Pnr
= (2500 × 4 × 5)/100
= Tk. 500