a; 472 + 54 + 361 + 28
= (472 + 28) + (54 + 361)
= 500 + 415
= 915
b; 817 + 251 + 423 + 349
= (817 + 423) + (251 + 349)
= 1240 + 600
= 1840
a) 472+54+361+28
=(472+28)+(361+54)
= 500+ 415
=915
b)817+251+423+349
=(817+423)+(251+349)
=1240+600
=1840