文档文本内容
四年级数学小数加减法的简便运算
★在小数加减法计算中运用整数加法运算律和减法的性质,使其能
够简便计算的关键在于凑十.凑整法.
加法交换律:a+b=b+a 加法结合律:(a+b)+c=a+(b+c)
整数减法的运算性质:①(a-b-c=a-(b+c) ②a-b-c=a-c-b
加法结合律
5.3+(17.13-4.7)+0.87 0.57+13.36+1.43+6.64 14.15-4.75+1.85-2.25
=5.3+17.13-4.7+0.87 =(0.57+1.43)+(13.36+6.64) =14.15+1.85-4.75-2.25
=(5.7-4.7)+(17.13+0.87) =2+20 =(14.15+1.85)-(4.75+225)
=0.6+18 =22 =16-7
=18.6 =9
7.84+3.16-7.84+3.16 18.75-6.5-8.75-3.5 14.7+5.9-14.7+5.9
=(7.84-7.84)+(3.16+3.16) =(18.75-8.75)-16.5+3.5) =(14.7-14.7)+(5.9+5.9)
=0+6.32 =10-10 =0+11.8
=6.32 =0 =11.8
减法运算性质
35.65-(18.65+4.15) 9.21-6.05-0.95 18.917-(4.917+5.73)
=35.65-18.65-4.15 =9.21-(6.05+0.95) =18.917-4.917-5.73
=17-4.15 =9.21-7 =14-5.73
=12.85 =2.21 =8.27
58.92-15.5-18.92-4.5
=(58.92-18.92)-(15.5+45)
=40-20
=20
1/17四年级数学小数简便计算专项练习
1.计算下面各题(能简算的要简算)。
6.78+2.04+7.22+5.96 0.25×4.4 2.8×101-2.8
2.计算下面各题，怎样简便就怎样计算。
1.29-3.7+9.71-6.3 300-2730÷91-70 400-(1300÷65+35)
125×48 6.45-(2.31-1.55) 64×39+37×39-39
3.怎样简便就怎样计算。
103×87-93×87 3000÷125÷8
6.74+12.62+24.38+3.26 23.4-8.54-1.46
2/176.92-(3.2+1.92) 101×78-78
4.怎样算简便怎样。
(1)5.02-3.5+0.98 (2)2.88+2.3+4.7 (3)7300÷(73×25)
(4)1050÷15÷7 (5)80-12.4-7.6 (6)568-(68+178)
5.简便运算。
3.27+5.49-1.27+4.51 9.75-(6.75+0.4)
10.27-0.34+1.73-2.66 12.457-(2.457-4.5-5.5)
3/177 用简便方法计算。
①25×1.25×32 ②(3.75-2.9+2.25)÷31%
8.用你喜欢的方法计算
5/8+3/4×60% 12.5×25%×20+3.2
0.875×25+75×87.5%+87.5 6.7-3.25+13.3-0.75
9、计算下面各题。你认为怎样简便就怎样算。
1.2÷2.5 ( 30.5-8.22)×0.4 34.7÷12.5÷0.8
10.能简算的要简算。
125%-68%+0.7 (45%+25%)×4 34%+79%+21%+66%
4/17120%+89%+11% 2-45%-55% 36%×1.7+1.7×64%
11.计算下面各题，怎样简便怎样计算，要写出必要的计算过程。
①10-2.8-7.2 ②16.8÷0.5÷2 ③3.7×0.25×4
12.怎样算简便就怎样算。
25.86+7.8-5.86 0.8×3.37×12.5 3.2+6.8×1.25×8
918-(107+218) 45×98 25×(20+4)
13.计算下面各题，怎样算简便就怎样算。
8.49+(4.64-2.14)×0.64 4.2×99+4.2
5/17四年级数学小数简便计算专项练习
1.计算下面各题(能简算的要简算)。
6.78+2.04+7.22+5.96 0.25×4.4 2.8×101-2.8
=(6.78+7.22)+(2.04+5.96) =0.25×4+0.25×0.4 =2.8×(101-1)
=14+8 =1+0.1 =2.8×100
=22 =1.1 =280
2.计算下面各题，怎样简便就怎样计算。
1.29-3.7+9.71-6.3 300-2730÷91-70 400-(1300÷65+35)
=1.29+9.71-(3.7+6.3) =300-30-70 =400-(20+35)
=11-10 =300-(30+70) =400-55
=1 =200 =345
125×48 6.45-(2.31-1.55) 64×39+37×39-39
=125×8×6 =6.45-2.31+1.55 =39×(64+37-1)
=1000×6 =6.45+1.55-2.31 =39×100
=6000 =8-2.31 =3900
3.怎样简便就怎样计算。
103×87-93×87 3000÷125÷8
=(103-93)×87 =3000÷(125×8)
=10×87 =3000÷1000
=870 =3
6.74+12.62+24.38+3.26 23.4-8.54-1.46
=(6.74+3.26)+(12.62+24.38) =23.4-(8.54+1.46)
=10+37 =23.4-10
=47 =13.4
6/176.92-(3.2+1.92) 101×78-78
=6.92-1.92-3.2 =(101-1) ×78
=5-3.2 =100×78
=1.8 =7800
4.怎样算简便怎样。
(1)5.02-3.5+0.98 (2)2.88+2.3+4.7 (3)7300÷(73×25)
=(5.02+0.98)-3.5 =2.88+(2.3+4.7) =7300÷73÷25
=6-3.5 =2.88+7 =100÷25
=2.5 =9.88 =4
(4)1050÷15÷7 (5)80-12.4-7.6 (6)568-(68+178)
=1050÷(15×7) =80-(12.4+7.6) =568-68-178
=1050÷105 =80-20 =500-178
=10 =60 =322
5.简便运算。
3.27+5.49-1.27+4.51 9.75-(6.75+0.4)
=3.27-1.27+(5.49+4.51) =9.75-6.75-0.4
=2+10 =3-0.4
=12 =2.6
10.27-0.34+1.73-2.66 12.457-(2.457-4.5-5.5)
=10.27+1.73-(0.34+2.66) =12.457-2.457+(4.5+5.5)
=12-3 =10+10
=9 =20
7/177.用简便方法计算。
①25×1.25×32 ②(3.75-2.9+2.25)÷31%
=25×1.25×4×8 =(3.75+2.25-2.9)÷31%
=(25×4)×(1.25×8) =(6-2.9)÷0.31
=100×10 =3.1÷0.31
=1000 =3.41
8.用你喜欢的方法计算
5/8+3/4×60% 12.5×25%×20+3.2
=5/8+3/4×3/5 =12.5×¼×20+3.2
=5/8+9/20 =62.5+3.2
=4340 =65.7
0.875×25+75×87.5%+87.5 6.7-3.25+13.3-0.75
=0.875×25+75×0.875+0.875×100 =(6.7+13.3)-(3.25+0.75)
=0.875×(25+75+100) =20-4
=0.875×100×2 =16
=175
9.计算下面各题。你认为怎样简便就怎样算。
1.2÷2.5 ( 30.5-8.22)×0.4 34.7÷12.5÷0.8
=(1.2×4)÷(2.5×4) =22.28×0.4 =34.7÷(12.5×0.8)
=4.8÷10 =8.912 =34.7÷10
=0.48 =3.47
8/1710.能简算的要简算。
125%-68%+0.7 (45%+25%)×4 34%+79%+21%+66%
=1.25-0.68+0.7 =(0.45+0.25)×4 =0.34+0.79+0.21+0.66
=0.57+0.7 =0.7×4 =(0.34+0.66)+(0.79+0.21)
=1.27 =2.8 =1+1=2
120%+89%+11% 2-45%-55% 36%×1.7+1.7×64%
=1.2+0.89+0.11 =2-0.45-0.55 =0.36×1.7+1.7×0.64
=1.2+(0.89+0.11) =2-(0.45+0.55) =(0.36+0.64)×1.7
=1.2+1 =2-1 =1×1.7
11.计算下面各题，怎样简便怎样计算，要写出必要的计算过程。
①10-2.8-7.2 ②16.8÷0.5÷2 ③3.7×0.25×4
=10-(2.8+7.2) =16.8÷(0.5×2) =3.7×(0.25×4)
=10-10 =16.8÷1 =3.7×1
=0 =16.8 =3.7
12.怎样算简便就怎样算。
25.86+7.8-5.86 0.8×3.37×12.5 3.2+6.8×1.25×8
=25.86-5.86+7.8 =(0.8×12.5)×3.37 =3.2+6.8×(1.25×8)
=20+7.8 =10×3.37 =3.2+6.8×10
=27.8 =33.7 =3.2+68
918-(107+218) 45×98 25×(20+4)
=918-107-218 =45×(100-2) =25×20+25×4
=918-218-107 =45×100-45×2 =500+100
=700-107 =4500-90 =600
9/1713.计算下面各题，怎样算简便就怎样算。
8.49+(4.64-2.14)×0.64 4.2×99+4.2
=8.49+2.5×0.64 =4.2×(99+1)
=8.49+2.5×4×0.16 =4.2×100
=8.49+10×0.16 =420
10/17
