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      Question

      An amount becomes Rs. 11,520 after 3 years at a simple

      interest rate of r% p.a. If the rate had been increased to (r + 5)% per annum, the same sum would become Rs. 12,570 in 3 years. Calculate the original sum invested.
      A Rs.7000 Correct Answer Incorrect Answer
      B Rs.5720 Correct Answer Incorrect Answer
      C Rs.6620 Correct Answer Incorrect Answer
      D Rs.4700 Correct Answer Incorrect Answer

      Solution

      ATQ,

      Let the sum invested be Rs. ‘P’.

      Simple interest at r% = 11520 – P

      So, 11520 – P = P × 3 × r ÷ 100

      Or, 100 × (11520 – P) = 3Pr ………. (I)

      Simple interest at (r + 5)% = 12570 – P

      So, 12570 – P = P × (r + 5) × 3 ÷ 100

      Or, 100 × (12570 – P) = 3Pr + 15P ………. (II)

      From (I) and (II),

      1257000 – 100P = 1152000 – 85P

      Or, 105000 = 15P

      P = 7000

      Therefore, sum = Rs. 7,000

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