The simple interest on a sum of money invested for a period of 10 years is equal to $$\frac{4}{5}$$th of the sum invested. What is the rate of simple interest per annum that is being given?
Let's assume the sum invested, rate of interest and time are 'P', 'R' and 'T'.
The simple interest on a sum of money invested for a period of 10 years is equal to $$\frac{4}{5}$$th of the sum invested.
$$\frac{P\times\ R\times\ T}{100}\ =\ \frac{4P}{5}$$
$$\frac{P\times\ R\times10}{100}\ =\ \frac{4P}{5}$$
$$\frac{1\times\ R\times1}{10}\ =\ \frac{4}{5}$$$$R\ =\ \frac{40}{5}$$
So the rate of simple interest per annum that is being given = R = 8%
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