Question

    At the rate of any compound interest rate, it gets

    tripled in 4 years, in how many years it will become 2187 times its own?
    A 22 Correct Answer Incorrect Answer
    B 26 Correct Answer Incorrect Answer
    C 28 Correct Answer Incorrect Answer
    D 24 Correct Answer Incorrect Answer

    Solution

    Let the principal be Rs. x, then Amount = 3x As we know, A = P (1+r/100)t 3x = x (1 + r/100)4 (1+r/100) = 4√3        ...i) Again, A = 2187x, P = x 2187x = x (1 + r/100)t (1+r/100) = t√2187   ...ii) From equation (i) 4 √3= t√2187 31/4 = 37/t Compare on powers 1/4 = 7/t t = 28 years Smart Approach-        In 4th year = 3 times.   After T   years =2187=37 T=4×7=28 years.

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