Dyscalculia

Dyscalculia is the medical term for experiencing severe difficulty in making arithmetical calculations, as a result of a brain disorder.

Prevalence

 * 71.6% - 75.1% of the 2073 patients in a Belgian study of 2001 reported difficulty with calculations.
 * Katrina Berne reports a prevalence of 75-80% for 'aphasia' (inability to find the right word, saying the wrong word) and/or dyscalculia (difficulty with numbers) - although she notes that this symptom is probably underreported and more prevalent than indicated.