(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
