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    Question

    An amount of Rs. ‘y’ was invested on (R-2)% per

    annum on simple interest and at the end of 6 years an amount of Rs. 23100 was obtained as an interest. If the amount was Rs. 7000 more and the rate of interest was ‘R’% per annum on simple interest, then at the end of 4 years an amount of Rs. 22320 was obtained as an interest. Find out the compound interest obtained on Rs. (y-5000) at the rate of (R+1)% per annum compounded annually for the period of 2 years. The value of ‘R’ is a natural number.
    A Rs. 8600 Correct Answer Incorrect Answer
    B Rs. 11400 Correct Answer Incorrect Answer
    C Rs. 12500 Correct Answer Incorrect Answer
    D Rs. 10500 Correct Answer Incorrect Answer
    E Rs. 14000 Correct Answer Incorrect Answer

    Solution

    An amount of Rs. ‘y’ was invested on (R-2)% per annum on simple interest and at the end of 6 years an amount of Rs. 23100 was obtained as an interest.

    y x (R-2)% x 6 = 23100

    y x (R-2) = 385000

    y = 385000/(R-2)    Eq.(i)

    If the amount was Rs. 7000 more and the rate of interest was ‘R’% per annum on simple interest, then at the end of 4 years an amount of Rs. 22320 was obtained as an interest.

    (y+7000) x R% x 4 = 22320

    (y+7000) x R = 558000    Eq.(ii)

    Put Eq.(i) in Eq.(ii).

    [{385000/(R-2)}+7000] x R = 558000

    After solving the above equation, R  = 9 .

    Put the value of ‘R’ in Eq.(i).

    y = 385000/(9-2)

    = 385000/7

    y = 55000

    Required compound interest = (y-5000) of (100+R+1)% of (100+R+1)% - (y-5000)

    Put the values of ‘y’ and ‘R in the above equation.

    = (55000-5000) of (100+9+1)% of (100+9+1)% - (55000-5000)

    = 50000 of 110% of 110% - 50000

    = 60500 - 50000

    = Rs. 10500

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