Litwiller, Bonnie H, Activities for the maintenance of computational skills and the discovery of patterns /Bonnie H. Litwiller and David R. Duncan. - Reston, Virginia : National Council of Teachers of Mathematics, (c)1980. - iv, 92 pages : illustrations ; 28 cm. LCCN: 80019773 Subjects--Topical Terms: Arithmetic--Problems, exercises, etc. LC Class. No.: QA139 / .A285 1980