Final answer:
The expression 20 - 9 : 3 simplifies to 20 - 3, which equals 17. None of the options provided by the student are correct as they do not list the answer as 17.
Step-by-step explanation:
The student's question pertains to the order of operations in a mathematical expression. The given expression is 20 - 9 : 3, where ':' represents the division operator. According to the order of operations, commonly known as PEMDAS (Parentheses, Exponents, Multiplication and Division from left to right, Addition and Subtraction from left to right), we must perform the division before the subtraction. Therefore, this expression simplifies as:
20 - (9 ÷ 3) = 20 - 3 = 17.
So, none of the options A, B, C, or D given by the student are correct, as the correct answer is 17 which is not listed. This misunderstanding might come from a typo on the question or the answer choices provided.