The difference of 10 and $u$ is expressed mathematically as:

$10 - u$

This expression represents subtracting $u$ from 10.

Would you like any details or have any questions?

Here are 5 related questions to explore:

1. What happens if $u$ is greater than 10?
2. How would you express the sum of 10 and $u$?
3. Can you solve $10 - u = 5$ for $u$?
4. What would the expression be if you wanted the difference of $u$ and 10 instead?
5. How would this expression change if both 10 and $u$ were multiplied by 2?

Tip: Understanding basic algebraic expressions is crucial for solving more complex equations. Start by mastering simple operations like addition, subtraction, multiplication, and division with variables.