<h1>12, medium. I know the solution to these problem types are really simple, but I can never remember exactly what to do… I can never think about these ones the right way.</h1>
<p>There are 25 trays on a table in the cafeteria. Each tray contains a cup only, a plate only, or both a cup and a plate. If 15 of the plates contain cups and 21 of the trays contains plates, how many contain both a cup and a plate?</p>
<h1>18, hard.</h1>
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<p>Hate these types too.</p>
<p>If you know of any similar problems, let me know please!</p>
<p>Thanks.</p>