₹ x invested at 9% simple interest per annum for 5 years yields the same interest as that on ₹ y invested at 6.25% simple interest per annum for 8 years. Find x : y.
Interest earned on Rs.x at 9% per annum for 5 years = $$\dfrac{x \times 9 \times 5}{100} = \dfrac{9x}{20}$$
Interest earned on Rs.y at 6.25% interest for 8 years = $$\dfrac{y \times 6.25 \times 8}{100} = \dfrac{50y}{100} = \dfrac{y}{2}$$
Given, $$\dfrac{9x}{20} = \dfrac{y}{2}$$
=> 18x = 20y
=> $$\dfrac{x}{y} = \dfrac{20}{18} = \dfrac{10}{9}$$
Hence, x : y = 10 : 9
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