An office worker mails 25 envelopes to customers each day. Every envelope contains 3 reports with a paper clip contains 3 report with a paper clip on each one. The supply of paper clip is provided in boxes of 500. How many days will it take for the clerk to use up one box of paper clips?
The office worker mails a total of 25 envelopes each day, and each envelope contains 3 reports with a paper clip on each one, so the worker uses 25 * 3 = <<25*3=75>>75 paper clips each day.
A box of paper clips contains 500 paper clips, so it will take the office worker 500 / 75 = <<500/75=6.67>>6.67 days to use up one box of paper clips.
Since the clerk cannot use up the box of paper clips in a fraction of a day, it will take the clerk 7 days to use up one box of paper clips. Answer: \boxed{7}.