法分配律:a×(b+c)=a×b+a×c ( a+b)×c =a×c +b ×c
(1)25×(40+4)
=25×40+25×4
=1000+100
=1100
(2)25×(40-4)
=25×40-25×4
=1000-100
=900
(3)25×102
=25×(100+2)
=25×100+25×2
=2500+50
=2550
(4)25×98
=25×(100-2)
=25×100-25×2
=2500-50
=2450
(5)73×25+27×25
=(73+27)×25
=100×25
=2500
(6)121×25-21×25
=(121-21)×25
=100×25
=2500
(7)99×25+25
=99×25+25×1
=(99+1)×25
=100×25
=2500
(8)25×16+25×82+25×2
=25×(16+82+2)
=25×100
=2500
(9)25×192-25-25×91
=25×192-25×1-25×91
=25×(192-1-91)
=25×100
=2500
(10)25×131-25×33+25×2
=25×(131-33+2)
=25×100
=2500
二
121+73+27+79
=(121+79)+(73+27)
=200+100
=300
三
(1)125×37×8
=125×8×37
=1000×37
=37000
(2)125×4×8×25
=(125×8)×(4×25)
=1000×100
=10000
四减法运算性质
(1)减法两数等减两数(凑整数)
561-73-27
=561-(73+27)
=561-100
=461
(2)减法两数等分减两数
921-(121+39)
=921-121-39
=800-39
=761
五加减混合
(1)183-47+17
=183+17-47
=200-47
=153
(2)195+47-95+53
=195-95+47+53
=100+(47+53)
=100+100
=200
六法(连)
(1)两数等两数积
6300÷25÷4
=6300÷(25×4)
=6300÷100
=63
(2)两数积等分两数
6300÷(63×4)
=6300÷63÷4
=100÷4
=25
七
450×61÷45
=450÷45×61
=10×61
=610
八括号方法
()加减法(级运算)(括号前面+号掉括号变号)
① 172+(28+69)
=172+28+69
=200+69
=269
② 195+(172-95)
=195+172-95
=195-95+172
=100+172
=272
(二)法级运算(括号前面×号掉括号变号)
① 125(8×9)
=125×8×9
=10009
=9000
② 45×(180÷45)
=45×180÷45
=1×180
=180
(三)(括号前面-号掉括号变号)
① 295-(61+95)
=295-61-95
=295-95-61
=200-61
=139
② 260-(78-40)
=260-78+40
=260+40-78
=300-78
=222
(四)(括号前面÷号掉括号变号)
① 6900÷(69×25)
=6900÷69÷25
=100÷25
=4
② 6900÷(69÷23)
=6900÷69×23
=100×23
=2300
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