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    Question

    If a sum when placed at compound interest grows to

    Rs.6,400 in 2 yrs and to Rs. 8,000 in 3 yrs, find the rate percent p.a.
    A 22% Correct Answer Incorrect Answer
    B 35% Correct Answer Incorrect Answer
    C 32% Correct Answer Incorrect Answer
    D 25% Correct Answer Incorrect Answer
    E None of these Correct Answer Incorrect Answer

    Solution

    Let the principal be P. ∴ P + CI for 3 yrs = Rs. 8,000         ----- (i) And P + CI for 2 yrs = Rs. 6,400    ----- (ii) Subtracting (ii) from (i), we get CI for the 3rd yr = 8,000 – 6,400 = Rs. 1600 Thus, CI calculated in the 3rd yr is basically the interest on the amount generated after 2 yrs which is Rs. 6,400. ∴R = (SI×100)/(P×T) = (1600×100)/(6400×1)  = 25 % p.a.

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