Proportions represent a part out of a whole.  10 red socks out of 13 total socks (10/13) is a proportion. Proportions can be solved by the means-extreme property.

    (1) I have 6 prodigy, 2 chemical brothers, and 4 kmfdm cds.  What is the proportion of chemical brothers cds to my total collection of cds?

    (2) 6 chairs are always placed with every 2 tables at FleetStreet High School.  Supposing a room has 72 chairs, how many tables does it have?

    (3) 19,548 books fit on a wall of the New Alexandrian Library.  There are 6 bookshelves on this wall, and every bookshelf holds the same number of books.  Supposing that another wall has 13 bookshelves; how many books can it hold?