A certain sum amounts to ₹5,200 in 2 years and ₹6,400 in 4 years at simple interest. What is the rate of interest per annum?
15 percent
Let the principal be \(P\) and the annual simple interest be \(I\).
From the given conditions: \(P + 2I = 5200\) and \(P + 4I = 6400\).
Subtracting the first equation from the second: \(2I = 1200 \Rightarrow I = 600\).
Substituting back: \(P = 5200 - 2 \times 600 = 4000\).
Rate of interest \(= \frac{I \times 100}{P} = \frac{600 \times 100}{4000} = 15\%\).
Hence, the rate of interest per annum is 15 percent.
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