Final answer:
Statements A and B contain variables. Statement A has 'x' as the variable and statement B implies a variable with a question mark (?). Statements C and D do not have variables.
Step-by-step explanation:
Variables in mathematics are symbols that can take on different values. In the context of the student's question, the statements that contain variables are those with symbols that represent unknown quantities or values we are looking to find.
Let's look at the provided statements:
- A. 13-x=9: This statement contains a variable 'x', which represents a number that, when subtracted from 13, equals 9.
- B. ?+7=12: This statement implies a variable, typically shown as a letter (e.g., n or x), that when added to 7, equals 12.
- C. 1+6=7: This is a simple arithmetic statement with no variables.
- D. 15-5=__ : While this statement has a blank, it is not a variable per se but rather a placeholder for the result of the subtraction.
So, the statements containing variables are A and B, where 'x' and the question mark represent the variables. Remember, a variable is a symbol used to represent an unknown value in mathematical equations and expressions.