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    Question

    An amount of 'P' was invested at simple interest at the

    rate of (R - 2)% per annum. It becomes Rs. 7,200 in 4 years and Rs. 10,800 in 8 years. What is the value of 'R'?
    A 30 Correct Answer Incorrect Answer
    B 27 Correct Answer Incorrect Answer
    C 44 Correct Answer Incorrect Answer
    D 56 Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    ATQ,

    Interest earned in 4 years = 10,800 - 7,200 = Rs. 3,600

    Interest earned in 4 years = Rs. 3,600 (already 4 years, no need to recalculate)

    Interest earned in 4 years = Rs. 3,600

    Interest in 4 years ⇒ Per year = 3,600 / 4 = Rs. 900

    Interest in 4 years = Rs. 3,600

    Interest in 4 years = Rs. 3,600

    Principal, 'P' = 7,200 - 900×4 = Rs. 3,600

    Now, using SI formula:

    3,600 = 3,600 × (R - 2) × 4 ÷ 100

    Or, 3,600 = 144 × (R - 2)

    Or, R - 2 = 3,600 ÷ 144 = 25

    So, 'R' = 25 + 2 = 27

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