Final answer:
The expression for the number of working pens in a pack is 'p - 2', where 'p' represents the total number of pens in the pack.
Step-by-step explanation:
The student has asked how to write an expression for the number of working pens in a pack if there are p pens in a pack and 2 of them do not work. To find the number of working pens, we subtract the 2 non-working pens from the total number of pens p.
The expression for the number of working pens would be: p - 2.
This is a simple algebraic expression that shows the total number of pens minus the ones that are not working, giving us the number of pens that are functioning properly.