To compare the numerical values **3.11** and **3.9**, follow these steps:
1. **Compare the Integer Parts**:
- Both numbers have the same integer part, which is **3**.
2. **Compare the Decimal Parts**:
- The decimal part of **3.11** is **0.11**.
- The decimal part of **3.9** is **0.90** (since **3.9 = 3.90**).
- Clearly, **0.90 > 0.11**, so **3.9 > 3.11**.
**Final Answer**:
\boxed{3.9\ \text{is greater}}