If an amount of Rs.80,000/- was kept in a book for a compound interest

If an amount of Rs.80,000/- was kept in a book for a compound interest at the rate of 10% per year to get an interest of Rs.16,800/-, then the amount was in the bank for a period of

  1. 3/2 years
  2. 2 years
  3. 5/2 years
  4. 3 years
Anurag Mishra Professor Asked on 19th April 2016 in Maths.
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  • 1 Answer(s)

    Answer: (2) 2 years

    Solution:-
    Principal = Rs.80,000, Rate = 10%, Compound Interest = Rs.16,800 & Time = ?

    Formula-
    Compound Interest = {Principal (Rate/100 + 1)Time – Principal}

    Then, 16,800 = {80,000(10/100 + 1)? – 80,000}
    16,800 = 80,000 {(11/10)? – 1}
    {(11/10)? – 1} = 16,800/80,000
    = 1680/8,000
    = 168/800
    = 42/200
    {(11/10)? – 1} = 21/100
    (11/10)? = 21/100 + 1
    (11/10)? = 121/100
    (11/10)? = (11/10)2
    ? = 2

    Then the amount was in the bank for a period of 2 years.

    Hence, the correct answer is option (2) 2 years.

    Anurag Mishra Professor Answered on 20th April 2016.
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