Answer:
495 chairs were set up.
Step-by-step explanation:
If a teacher asked the class to arrange C chairs in R rows then total number of chairs will be = C × R
If there are are 5 chairs short in the class set then number of chairs used
= (C × R) - 5
Now it has been given that number of chairs and number of rows are 25 and 20 then the chairs used will be
= (25 × 20) - 5
= 500 - 5
= 495
Therefore, 495 chairs were used in the class set up.