A Bumper Sticker 
for Math Aficionados
who drive Ford vehicles 

We know mathematicians have a slight tendency to be liberals
whereas Ford drivers have a strong tendency to be conservatives
(except maybe for C-Max drivers)
so this product has a very limted market.
We think this is a shame since Ford is the only car company
that allows you to unlock your car with a 5-digit code
such as the first 5 digits of your favorite sequence
or the only 5-digit prime Fibonacci number.
But it means that you will be really special if you buy it
and your car will be unique in your neighborhood!

The bumper sticker is 3¾" tall and 11¾" wide, with dark maroon printing on light gray, glossy vinyl. 
It is durable and UV-resistant and has an easy-to-peel backing.

What are Ford Circles?

Ford circles are named for American mathematician Lester R. Ford, Sr. (1886-1967), presumably
no relaton to American industrialist Henry Ford (1863-1947), founder of the Ford Motor Company.

At each rational point p/q (expressed in lowest terms) on the real number line,
there's a Ford circle of diameter 1/q² above and tangent to the line.
Between two such circles, at p/q and r/s, the circle at (p+r)/(q+s) will be tangent to both of them.
For example, as you can see on the bumper sticker, the circle at 5/7 is tangent to those at 2/3 and 3/4. 
This method of combining fractions - the way some young students wish they could add them -
is called Farey addition, and the sum is called the mediant.
Amazingly, although there is a Ford circle at every rational point, their interiors never intersect at all.

Ordering Information

The cost is $12 per sticker plus $4 S&H per order. California orders must include sales tax.
To order by check, send to SB Crafts at 6167 La Goleta Road, Santa Barbara, CA 93117.
To pay by credit card, just contact us and we'll invoice you.
For any questions, email info@SBCrafts.net or text 805-680-9950 or call 805-967-2270.