To determine if a variable x is greater than 10 and less than 20 at the same time, you need to use a logical AND condition.
The correct expression is:
10 < x && x < 20
This expression checks two conditions: first, it verifies that x is greater than 10, and second, it checks that x is less than 20. In many programming languages, the logical AND operator is represented by &&, which combines these two comparisons into a single Boolean expression. If both comparisons evaluate to true, then the overall expression is true, indicating that x lies within the desired range.