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      Question

      A certain amount grows to Rs. 9,240 in 6 years at a simple

      interest rate of r% per annum. If the rate had been (r + 2)% p.a., the amount would have become Rs. 9,840 in the same time. Find the original investment.
      A Rs.5000 Correct Answer Incorrect Answer
      B Rs.5720 Correct Answer Incorrect Answer
      C Rs.4620 Correct Answer Incorrect Answer
      D Rs.4700 Correct Answer Incorrect Answer

      Solution

      ATQ,

      Let the invested sum be Rs. ‘P’.

      Simple interest at r% = 9240 – P

      So, 9240 – P = P × 6 × r ÷ 100

      Or, 50 × (9240 – P) = 3Pr ………. (I)

      Interest at (r + 2)% = 9840 – P

      So, 9840 – P = P × (r + 2) × 6 ÷ 100

      Or, 50 × (9840 – P) = 3Pr + 6P ………. (II)

      Now using (I) and (II),

      492000 – 50P = 462000 – 44P

      Or, 30000 = 6P

      So, P = 5000

      Thus, original sum = Rs. 5,000

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