<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 trays contain cups and 21 of the trays contain plates, how many contain both a cup and a plate?</p>
<p>Is this a permutation problem? How would you do it simplest and fastest?</p>
<p>11 Would contain both.</p>
<p>this isnt a permutation prblem, its a ven diagram problem. Since theres 15 trays and 21 plates, thats more than the total trays. the 15 trays of cups and 21 trays of plates can contain both a cup and a tray. Thus you must subtract X, which i used to stand for trays that contain both. (15+21) - X = 25
Solve for X, which is 11.</p>
<p>Am i correct ? lol</p>
<p>seems right</p>
<p>Oh, whoa, that was so simple! Yeah you're correct..</p>
<p>I was doing 15-x=y, 21-x=z, x+y+z=25.... so stupid n confusing... lmao. thanks a bunch!</p>
<p>It makes sense to search for math questions on CC.
A search for "trays" on the SAT forum would bring this one up:
<a href="http://talk.collegeconfidential.com/sat-preparation/394895-help-me-solve-math-prob.html%5B/url%5D">http://talk.collegeconfidential.com/sat-preparation/394895-help-me-solve-math-prob.html</a></p>