00303nam a2200109Ia 450000500170000000800410001708200180005810000190007624500430009526000450013830000100018320260205040630.0260111s9999||||xx |||||||||||||| ||und||  a511.07  B212T  aBallard, P. B. 0aTeaching the essentials of arithmetic.  aLondonbUniversity of London Pressc1952  a260p.