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    Question

    A certain sum of money at simple interest amounts to Rs

    7200 in 3 years and Rs 8000 in 5 years. What is the rate of interest per annum?
    A 2â…”% Correct Answer Incorrect Answer
    B 6â…”% Correct Answer Incorrect Answer
    C 5â…”% Correct Answer Incorrect Answer
    D 9â…”% Correct Answer Incorrect Answer

    Solution

    ATQ, Let principal = P, rate = r per year. Amount after 3 years: P(1 + 3r) = 7200 Amount after 5 years: P(1 + 5r) = 8000 Divide second by first: (1 + 5r) / (1 + 3r) = 8000 / 7200 = 10/9 9(1 + 5r) = 10(1 + 3r) 9 + 45r = 10 + 30r 15r = 1 ⇒ r = 1/15 = 6⅔% per annum.

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