I always love it when people buy domains then request an "appraisal". It's almost as if they are hoping they paid the "right" amount for the domain.
However in your case George, whatever you paid for it you'll definitely get your money back five-fold--NEVER SELL THIS DOMAIN. This is one of those "priceless" dot com domains in that the branding of this domain is "free". Every child has to start learning math at an early age and doesn't stop until college unless they are engineers which could continue until age 65.
Anyways, Good luck with it George... Your plight to get this domain reminds me of my favorite quote: "The harder I work, the luckier I get."
P.S Get ready for "spikes" in traffic in January and September... I had a "math" site at one time and without fail I saw a marked increase in traffic during these months...The traffic mainly came from college students/parents/professors.