Question

用简便方法计算（有理数的减法）1小时之内得到答案，注意，要写下计算过程，谢谢，回答最佳着采纳

（1）－5／7－4／5－1／2＋3／4－2／7－1／5
＝
（2）2－7／12＋8／15＋1／12－11／15－23／20
＝
（3）81.35-282.9+8.65-7.1
=
(4)(-1/4)-(-1/2)-(-3/4)-(+1/8)+(-1/8)-(-2/3)

Answer 1

（1）－5／7－4／5－1／2＋3／4－2／7－1／5
＝－5／7－2／7－4／5－1／5＋3／4－1／2
=-(5/7+2/7)-(4/5+1/5)+(3/4-2/4)
=-1-1+1/4
=-7/5

（2）2－7／12＋8／15＋1／12－11／15－23／20
＝2-(7/12-1/12)+(8/15-11/15)-23/20
=2-1/2-1/5-23/20
=(40-10-4-23)/20
=-3/20

（3）81.35-282.9+8.65-7.1
=81.35-282.9+8.65-7.1
=(81.35+8.65)-(282.9+7.1)
=90-290
=-200

(4)(-1/4)-(-1/2)-(-3/4)-(+1/8)+(-1/8)-(-2/3)
=-1/4+1/2+3/4-1/8-1/8+2/3
=1/2+3/4-1/4-(1/8+1/8)+2/3
=1/2+2/4-2/8+2/3
=1/2+1/2-1/4+2/3
=1-1/4+2/3
=3/4+2/3
=17/12

Answer 2

（1）－5／7－4／5－1／2＋3／4－2／7－1／5
=(-5/7-2/7)+(-4/5-1/5)+(-1/2+3/4)
=-1-1+1/4
=-7/4
（2）2－7／12＋8／15＋1／12－11／15－23／20
=2+(-7/12+1/12)+(8/15-11/15)-23/20
=2-1/2-1/5-23/20
=3/20
（3）81.35-282.9+8.65-7.1
=(81.35+8.65)-(282.9+7.1)
=90-290
=-200
(4)(-1/4)-(-1/2)-(-3/4)-(+1/8)+(-1/8)-(-2/3)
=(-1/4+1/2+3/4)-(1/8+1/8)+2/3
=1-1/4+2/3
=17/12

Answer 3

解：1、 -5/7-4/5-1/2+3/4-2/7-1/5=（-5/7-2/7）+（-4/5-1/5）+（3/4-2/4）=-1-1+1/4=-7/4
2、 =2+（-7/12+1/12）+（8/15-11/15）-23/20=2-6/12-3/15-23/20=2-1/2-1/5-23/20=40/20-10/20-4/20-23/20=3/20
3、 =（81.35+8.65）+（-282.9-7.1）=90-290=-200
4、 =-1/4+1/2+3/4-1/8-1/8+2/3=（-1/4+1/2+3/4）+（-1/8-1/8）+2/3=1-1/4+2/3=17/12

Answer 4

（1）－5／7－4／5－1／2＋3／4－2／7－1／5
＝－5／7－2／7－4／5－1／5＋3／4－1／2
=-(5/7+2/7)-(4/5+1/5)+(3/4-2/4)
=-1-1+1/4
=-7/5

（2）2－7／12＋8／15＋1／12－11／15－23／20
＝2-(7/12-1/12)+(8/15-11/15)-23/20
=2-1/2-1/5-23/20
=(40-10-4-23)/20
=-3/20

（3）81.35-282.9+8.65-7.1
=81.35-282.9+8.65-7.1
=(81.35+8.65)-(282.9+7.1)
=90-290
=-200

Answer 5

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