The compound interest on a certain sum of money for 2 years at 10% per annum is TK. 420 . The simple interest on the same sum at the same rate and for same time will be?

The compound interest on a certain sum of money for 2 years at 10% per annum is TK. 420 . The simple interest on the same sum at the same rate and for same time will be? Correct Answer TK. 400

We know, C = P ( 1 + r)n Let, Pricipal P = x ∴ 420 + x = x (1 + 10100)2⇒420  + x  = x (1 + 0.1)2⇒420  + x  =  x(1.1)2⇒420  + x  = x ×1.21⇒420  +  x  =  1.21x⇒1.21x  - x  = 420 ⇒ (1.21  - 1)x  = 420 ⇒0.21 x  = 420 ⇒ x = 4200.21⇒ x = 420×10021⇒x = 2000 simple interest, I  = Prn  = 2000×10100×2 = 400
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