1) (637 +1004) + 996 = 637 +(1004 +996) = 637 + 2000 = 2 637
2) 729 + (47 + 271 ) = (729 + 271) +47 = 1000 +47 = 1047
3) 398989 + (201011 + 6482) = (398989 + 201011) + 6482 = 600000 + 6482 = 606482
4) 15824 + (37301 + 24176) = (15824 + 24176) + 37301 = 40000 + 37301 = 77301