Bihar Police Constable Model Paper 2

Let the principal be Rs. 100.
⇒ Amount = Rs. 200
S.I. = Amount – Principal = 200- 100 = Rs. 100
Time, T = 20 years
Rate of Interest, R = $\frac{\mathit{S}.\mathit{I}.\times 100}{\mathit{P}\times \mathit{T}}$
R = $\frac{100\times 100}{100\times 20}$ = 5%
Hence, required Rate of Interest = 5%.