a) 800 + 400 < 894 + 419 < 900 + 500 1200 < 894 + 419 = 1313 < 1400
б) 2000 + 6000 < 2849 + 6185 < 3000 + 7000 8000 < 2849 + 6185 = 9034 < 10000