(1)25×42×4

=(25×4)×42

=100×42

=42

(2)68×125×8

=68×(125×8)

=68×1000

=68000

(3)4×39×25

=(4×25)×39

=100×39

=3900

(4)4×25+16×25

=(4+16)×25

=20×25

=500

(5)4×25×16×25

=100×4×4×25

=100×4×100

=400×100

=40000

(6)36×99

=36×(100-1)

=36×100-36

=3600-36

=3564

(7)(25+15) ×4

=25×4+15×4

=100+60

=160

(8)(25×15)×4

=25×4×15

=100×15

=1500

(9)49×99+49

=49×(99+1)

=49×100

=4900

(10)(68+32)×5

=100×5

=500

(11)5×289×2

=(5×2)×289

=10×289

=2890

(12)68+32×5

=68+160

=220

(13)(125×25)×4

=125×25×4

=125×100

=12500

(14)(125+17)×8

=125×8+17×8

=1000+136

=1l36

(15)25×64×125

=25×4×4×8×125

=100×4×1000

=400×1000

=400000

(16)85×82＋82×15

=82×(85+15)

=82×100

=8200

(17)102×100+102

=102×100+100×1+2

=100×(102+1)+2

=100×103+2

=10300+2

=10302