1) 414 + 1952 + 586 = (414 + 586) + 1952 = 1000 + 1952 = 2952;
2) 4302 + (20700 + 5698) = (4302 + 5698) + 20 700 = 10000 + 20 700 = 30 700;
3) (358 + 373) + 4142 = (358 + 4142) + 373 = 4500 + 373 = 4873;
4) 417 + 488 + 583 + 1512 = (417 + 583) + (488 + 1512) = 1000 + 2000 = 3000.