Q. A sum of money amounts to 5200 Rs. in 5 years and to 5680 Rs. in 7 years at simple interest. The rate of interest per annum is :
Answer: 6%
Notes: P + SI for 5 years = 5200…………(I) P + SI for 7 years = 5680…………(II) On subtracting equation (I) from (II) SI for 2 years = 480 ∴ SI for 1 years = 240 ∴ From equation (I), P + 5 $latex \times$ 240 = 5200 $latex => P = 5200 - 1200 = 4000 Rs.$ $latex \therefore R = \frac{SI\times 100}{T\times P}&s=1$ $latex = \frac{240\times 100}{1\times 4000} = 6\%&s=1$ Hence option [D] is correct answer.

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