ІІ ЧАСТИНА. I. Тисяча » 80-81

80. 800 – 500 – 100 = 200; 200 + 300 + 400 = 900; 900 + 90 + 9 = 999; 800 + 80 + 7 = 887; 400 + 1 = 401; 400 – 1 = 399. 81. 600 – 400 = 200; 400 – 1 = 399; 799 + 1 = 800; 999 – 99 = 900; 400 + 1 = 401; 400 + 40 = 440.