Argh, my friend explained the puzzle to me wrong. Let’s try again.
You have a rectangular table. On the table you have a bunch of quarters arranged such that if you were to place an additional quarter anywhere on the table, it would overlap with at least one quarter already on the table. You can “place” a quarter if the center of the quarter is on the table, so a placed quarter can be partly off the table.
Say the number of quarters on the table is X. Using a simple, one sentence explanation, prove that with 4X quarters you could cover the entire table so that no table is showing – it’s completely covered by quarter.