Perhaps the publisher thought that "category theory" might not work well for American audiences?
http://smile.amazon.com/How-Bake-Pi-Exploration-Mathematics/...
I seem to collect mathematics books. However this is still my favourite book on mathematics and only because it was written by a surgeon rather than a mathematician: http://www.goodreads.com/book/show/383087.Mathematics
Warning: Took me a couple of years to get through.
Oh and 1946 copy of Calculus for the Practical Man by J E Thompson.
Plus if you need a .pdf of Feynman's favorite math book (Calculus for the Practical Man - Thompson (1946)) currently there are copies at KAT and PB.
Grab the nearest popcorn and watch the gender wars unfold.
Hannah has 6 orange sweets and some yellow sweets. Overall, she has n sweets. The probability of her taking 2 orange sweets is 1/3. Prove that: n^2-n-90=0.
If a HS student I would imagine you would
First: think of coins p(H1) = .5; p(H2) =.5; p(H1+H2) = .5 * .5 = .25
Second: OK, here (6/n) * (5/(n-1)) = 1/3
Third solve: 30/(n * (n-1)) = 1/3
90 = n^2 - n
0 = n^2 - n - 90
n=10 or -9; if -9 then Hannah only has one sweet and lifted 9 from somebody else just to demo her point.(from London Telegraph today)
C(6,2) / C(n,2) = 1/3
(where C(n,k) is n choose k) 15 / [n(n-1)/2] = 1/3
30 / n(n-1) = 1/3
n(n-1) = 90
I probably wouldn't have done that in high school, though.