Expression Word Problem

A group of students are talking. 2 friends leave the group. Write an expression for the number of students in the group after the 2 leave...
Answer: S-2 or G-2
Because, the question says "a group of students" it does not tell us how many students are in the group. Therefore we use a variable since the number is unknown.
And, 2 because the question states that 2 students leave the group.
S = students and G = group

You can use either one.