If the difference between the simple interest and compound interests on some principal amount at 20% for 3 years is Tk. 48, then the principal amount is -

Let the sum be Tk. x
Amount after 3 years on Tk. x at 20% per annum when interest is compounded annually
P(1 + R/100)^T
= x{1 + (20/100)}³
= x(120/100)³
= x(6/5)³
Compound interest = {x(6/5)³ - x}
= x{(6/5)³ - 1}
= x{(216/125) - 1}
= 91x/125
Simple interest PRT/100 = (x × 20 × 3)/100
= 3x/5
Given that difference between compound interest and simple interest is Tk. 48
(91x/125) - (3x/5) = 48
⇒ (91x - 75x)/125 = 48
⇒ 16x/125 = 48
⇒ x = (48 × 125)/16
= 3 × 125
= Tk. 375.