\[\text{The formula for total credit is: } \text{Total Credit} = \frac{\text{Primary Deposits}}{\text{Reserve Ratio}}.\]
\text{Substitute the values:}
\[500 = \frac{X}{0.20}, \quad \text{where X is the primary deposits.}\]
\text{Solving for X:}
\[X = 500 \times 0.20 = ₹ 100.\]