a)
37+194+63
= (37+63)+194
= 100 + 194
= 294
b)
36 × 23 + 23 × 64 + 120
= ( 64 +36 ) × 23 + 120
= 100 × 23 + 120
= 230 + 120
= 350
c)
28 × 71 + 28 × 64 - 28 × 35
= 28 × ( 71 + 64 - 35 )
= 28 × 100
= 2800
d)
2+4+6+.....+28+30
= ( 2+ 28 )+(4+26)+(6+24)+(8+22)+(10+20)+(12+18)+(14+16)+15+30
=30+30+30+30+30+30+30+30+15
=240+15
=255
Hay nhất !!^^