a) (7357 + 2848) + 5152 = 7357 + (2848 + 5152) = 7357 + 8000 = 15357
б) (54 271 + 39 999) + 10 001 = 54 271 + (39 999 + 10 001) = 54 271 + 50 000 = 104271
в) 19 999 + (4801 + 15 200) = 19 999 + (15 200 + 4801) = (19 999 + 1) + (15 200 + 4800) = 20 000 + 20 000 = 40000
г) 18 356 + (1644 + 2135) = 18 356 + (2135 + 1644) = (18 356 + 1644) + 2135 = 20 000 + 2135 = 22135