Step 1: The sum of the parts of the ratio is:
\[ 3 + 4 + 5 = 12. \]
Step 2: The total house rent is ₹20,000, so the value of one part is:
\[ \frac{20,000}{12} = 1666.67. \]
Step 3: The least share is paid by the person who gets 3 parts, which is:
\[ 3 \times 1666.67 = 5000. \]
Conclusion: The least share paid among the three friends is ₹5,000.