SOLUTION TO EXERCISE 4

Looking up the population of the New York State, I find there are about
18 million people.  If each family has about
four people, and about one in five families has a cat, and each cat
has one litter box, that makes 18 * 10^6 / 4 / 5 / 1 = 900,000 boxes.

Now let's say each litter box is 12 inches by 24 inches and is filled 
to a depth of two inches.  (I asked a cat-owner friend for this info.)
It is generally known that a cubic inch of medium-coarse sand contains
about 10,000 grains; if you didn't know this, you could lay grains
of sand on a ruler to see how many there are per inch and then cube
the result.  Coarse sand is about 1000 grains per cubic inch, and 
fine sand is about 100,000 grains per cubic inch.  Pick your size!

(Or you could search on the WWW - for example, on Yahoo.com you can
do a composite search like ["grains of sand" per cubic inch] - and find
a site like http://www.netaxs.com/~sparky/what_is_sand.html, which
explains that sand is soil that contains primarily grains between
0.075 and 4.75 millimeters; then you can pick a number between those
that sounds reasonable, use 1 inch = 25.4 millimeters as a conversion,
and compute the number of grains per cubic inch.)

Anyhow, kitty litter is like coarse sand, so I'll use 1000 grains/in^3.
That means that there are

900,000 boxes * (12 * 24 * 2) in^3/box * 1000 grains/in^3 = 5.2 * 10^11 
    
or about 500 billion grains of kitty litter in New York.  This is about
five times larger than our estimate of the number of stars in the Milky
Way galaxy.