The expression for "the sum of twice a number and seven" can be written as:

$2x + 7$

where $x$ represents the unknown number.

Would you like further details or examples on how to work with this expression?

Here are 5 related questions:

1. What happens if the sum of twice a number and seven equals a specific value (e.g., 15)?
2. How do you solve $2x + 7 = 21$?
3. Can you generalize the process to solve $2x + 7 = y$ for any $y$?
4. What would the sum of three times a number and seven be?
5. How does the expression change if instead of seven, we add five?

Tip: Always try to translate word problems into algebraic expressions to make them easier to solve!