加减简便运算
加法交换律:a +b=b+a 加法结合律:(a +b )+c=a+(b +c )
例1:213+46+54 例2:100―9.8―9.7―9.5
=213+(46+54) =100-10×3+(0.2+0.3+0.5) =213+100 =71 =313
例3:9+7+13 = 9+(7+13) 28-12-6 = 28-(12-6)
26+(24-8)= 26+24-8 80-(17+3)= 80-17+3
练习:
4392+2997 5364-1999 3.72-(1.72+1.3) 89-(899-25
) 3834-15.38+61.25-4.62 1323
13-2.25-74
14574178-211-111 823+514-61723
+0.75 13.76-(712+1.76+1512) (85447
12+37)-(7-12
)
例4:1+2+3+……+99+100
=(1+100)×
100
2
=101×50 =5050
例5:100+99+98-97-96+95+94-93-92+……+7+6-5-4+3+2-1
=100+2×100-4
2
+3+2-1 =200
练习:
99-97+95-93+91-89+……+7-5+3-1
12001+22001+32001+42001+……+2001
2001
1+2+3-4+5+6+7-8+9+10+11-12+……+25+26+27-28
2006—
12006—232006
2006—2006—……—2006
1-112-4-18-116-1132-……-1024
练习:
5.73+3.2+1.26 1.37+0.46+0.63+4.54
36.28-4.83-6.17 10.26-(3.78+4.26) [1**********]2+++……++ 9+99+999+9999+2
[**************]
12.8+8.6-12.8+8.6
613-611+713-511 1
16-(16+78) 3
2107
9-11+9
415-(415-23
) 519+48-5
9
9.75+99.75+999.75+9999.75 8-2
15-145
(2+4+6+……+100)-(1+3+5+……+99)
加减简便运算
加法交换律:a +b=b+a 加法结合律:(a +b )+c=a+(b +c )
例1:213+46+54 例2:100―9.8―9.7―9.5
=213+(46+54) =100-10×3+(0.2+0.3+0.5) =213+100 =71 =313
例3:9+7+13 = 9+(7+13) 28-12-6 = 28-(12-6)
26+(24-8)= 26+24-8 80-(17+3)= 80-17+3
练习:
4392+2997 5364-1999 3.72-(1.72+1.3) 89-(899-25
) 3834-15.38+61.25-4.62 1323
13-2.25-74
14574178-211-111 823+514-61723
+0.75 13.76-(712+1.76+1512) (85447
12+37)-(7-12
)
例4:1+2+3+……+99+100
=(1+100)×
100
2
=101×50 =5050
例5:100+99+98-97-96+95+94-93-92+……+7+6-5-4+3+2-1
=100+2×100-4
2
+3+2-1 =200
练习:
99-97+95-93+91-89+……+7-5+3-1
12001+22001+32001+42001+……+2001
2001
1+2+3-4+5+6+7-8+9+10+11-12+……+25+26+27-28
2006—
12006—232006
2006—2006—……—2006
1-112-4-18-116-1132-……-1024
练习:
5.73+3.2+1.26 1.37+0.46+0.63+4.54
36.28-4.83-6.17 10.26-(3.78+4.26) [1**********]2+++……++ 9+99+999+9999+2
[**************]
12.8+8.6-12.8+8.6
613-611+713-511 1
16-(16+78) 3
2107
9-11+9
415-(415-23
) 519+48-5
9
9.75+99.75+999.75+9999.75 8-2
15-145
(2+4+6+……+100)-(1+3+5+……+99)