On what principal at the rate of 10% per annum :

On what principal at the rate of 10% per annum, the difference between the compound interest for 3 years and 2 years is Rs.121.00?

  1. Rs.1,000
  2. Rs.1,200
  3. Rs.1,500
  4. Rs.2,000
Anurag Mishra Professor Asked on 17th December 2015 in Maths.
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  • 1 Answer(s)

    Answer:  (1) Rs. 1, 000

    Solution:-
    Let the principal be Rs.X

    Formula-
    Compound Interest = P [(1 + R/100)t – 1]
    Where, P = principal, R = rate, t = time.

    If the difference between the compound interest for 3 years and 2 years.
    Then,
    X {(1 + 10/100)3 – 1} – X {(1 + 10/100)2 – 1} = 121.00
    X [{(11/10)3 – 1} – {(11/10)2 – 1} = 121.00
    X [{(1331 – 1000)/1000} – {(121 – 100)/100}] = 121
    X (331/100 – 21/100) = 121
    X (331 – 210)/1000 = 121
    X (121)/1000 = 121
    X = 121 x 1000/121
    X = 1,000

    Then principal is Rs.1, 000.

    Hence, the correct answer is option (1) Rs. 1, 000.

    Anurag Mishra Professor Answered on 17th December 2015.
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