Given:

Principal (P) = Rs. 1
Interest (I) = 1 Paisa = Rs. \(\frac1{100}\)
Time (T) = 1 Month = \(\frac1{12}\) year

To find:

Rate of interest (R) = ?

By formula,

\(R=\frac{I\times100}{P\times T}\)
= \(R=\frac{{\displaystyle\frac1{100}}\times100}{1\times{\displaystyle\frac1{12}}}\)
= \(R=\frac{12}1\)
= 12

∴ Rate of interest (R) = 12% is the required answer.