7
运用乘法结合律和交换律，使计算简便
$25 × (20 × 30) = ($$× $$) × $$ = ($$)$
$25 × (40 × 20) = ($$× $$) × $$ = ($$)$
$39 × 25 × 40 =$$× ($$× $$) = ($$)$
$(92 × 8) × 25 =$$× ($$× $$) = ($$)$
$20 × (5 × 23) = ($$× $$) × $$ = ($$)$
$5 × (29 × 6) = ($$× $$) × $$ = ($$)$
$4 × (25 × 48) = ($$× $$) × $$ = ($$)$
$(3 × 6) × 5 =$ $800 × (4 - 2) =$ $5 + 77 × 3 =$
$3 × (6 × 5) =$ $100 ÷ 50 × 2 =$ $30 + 636 ÷ 6 =$
$(8 × 6) × 5 =$ $6 × 300 + 4 =$ $10 + 1000 ÷ 100 =$
$8 × (6 × 5) =$ $500 + 7 × 3 =$ $101 + 10 × 10 =$
$15 × (5 × 6) =$ $30 + 360 ÷ 60 =$ $12 × 400 + 7 =$
$(15 × 5) × 6 =$ $8 × 2 + 800 ÷ 4 =$ $420 ÷ 70 × 5 =$
$25 × (2 × 30) =$ $202 + 7 × 7 =$ $720 ÷ 8 - 9 =$
$(25 × 2) × 30 =$ $(119 - 8) ÷ 3 =$ $290 × 2 + 2 =$
$18 × 5 × 2 =$ $150 ÷ 50 × 2 =$ $206 × 3 ÷ 2 =$
$18 × (5 × 2) =$ $6 × 903 + 4 =$ $210 × 30 - 8 =$
时间（）

25；20；30；15000
25；40；20；20000
39；25；40；39000
92；8；25；18400
20；5；23；2300
5；6；29；870
4；25；48；4800
90；1600；236
90；4；136
240；1804；20
240；521；201
450；36；4807
450；216；30
1500；251；81
1500；37；582
180；6；309
180；5422；6292
（ ）