Решение:
43 + 25 + 17 + 15 = (43 + 17) + (25 + 15) = 60 + 40 = 100
48 + 13 + 12 + 7 = 48 + (13 + 7) + 12 = 48 + 20 + 12 = 80
19 + 24 + 11 + 26 = (19 + 11) + (24 + 26) = 30 + 50 = 80
27 + 54 + 3 + 6 = 27 + 3 + 54 + 6 = 30 + 60 = 90