innumerate

from WordNet (r) 3.0 (2006)

innumerate
    adj 1: lacking knowledge and understanding of mathematical
           concepts and methods [ant: {numerate}]

from The Collaborative International Dictionary of English v.0.48

innumerate \innumerate\ adj.
   Lacking knowledge and understanding of mathematical concepts
   and methods; by analogy with {illiterate}. Opposite of
   {numerate}. Also See: {educated}; {illiterate}.
   [WordNet 1.5]