State which of the following are equations (with a variable). Give reason for your answer. Identify the variable from the equations with a variable.
`2n + 1 = 11`

Answer

### Step-by-Step Solution:

1. **Identify the given expression**: The expression provided is \( 2n + 1 = 11 \).

2. **Determine if it is an equation**: An equation is defined as a mathematical statement that asserts the equality of two expressions, which is indicated by the presence of an equal sign (=). In this case, we have the equal sign between \( 2n + 1 \) (left-hand side) and \( 11 \) (right-hand side).

**Conclusion**: Yes, \( 2n + 1 = 11 \) is an equation.

3. **Provide a reason for the conclusion**: The reason it is an equation is that it contains an equal sign, and both sides of the equation consist of terms. The left-hand side (LHS) is \( 2n + 1 \) and the right-hand side (RHS) is \( 11 \). Since both sides are equal, it satisfies the condition of being an equation.

4. **Identify the variable**: In the equation \( 2n + 1 = 11 \), the term \( n \) is a variable. A variable is typically represented by a letter (in this case, \( n \)) that can take different values.

**Conclusion**: The variable in the equation is \( n \).

### Summary of Answers:
- **Is it an equation?** Yes.
- **Reason:** It has an equal sign and both sides contain terms.
- **Variable identified:** \( n \).