Question

    A certain sum of money yields Rs. 8,334 as compound

    interest for 3 years at 15% per annum. Calculate the approximate compound interest on the same amount of sum for 4 years at 10 % per annum.
    A 9,500 Correct Answer Incorrect Answer
    B 8,425 Correct Answer Incorrect Answer
    C 7,500 Correct Answer Incorrect Answer
    D 7425 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the principal be Rs. x, Now, CI = P [ ( 1 + R/100 )ᵀ - 1] ⇒ 8334 = x [ ( 1 + 15/100 )³ - 1 ] ⇒ 8334 = x [ ( 115/100 )³ - 1 ] ⇒ 8334 = x ( 12167/8,000 - 1 ) ⇒ 8334 = x ( (12167 - 8,000)/8,000 )= 4167/8,000 x x = (8334 × 8,000)/4167 = Rs. 16,000 ∴ The principal amount is Rs. 16,000. Now, CI= 16,000 [ ( 1 + 10/100 )4 - 1] ⇒ CI = 16000 [ (11/10 )4 - 1 ] ⇒ CI = 16000 [ (14641/10000 ) - 1 ] ⇒ CI = 16000 [ 1.4641 - 1 ]= 16000 x 0.4641 ⇒ CI = 7425.6

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