Final answer:
The algebraic expression representing the amount each student needs to fundraise for a $280 instrument is 280/x, with x being the number of students.
Step-by-step explanation:
The algebraic expression to represent the amount that each student needs to fundraise is 280/x. This is because the total cost of the new instrument is $280 and it is to be divided equally among the x students. Each student's share of the cost will be the total cost divided by the number of students, which is represented by the expression 280/x.