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練習問題2(正の数・負の数加減法3)解答・解説

練習問題2(正の数・負の数加減法3)


(1) 7-12-4+10-15


  =(+7)+(-12)+(-4)+(+10)+(-15)


  =+(7+10)-(12+4+15)


  =(+17)+(-31)


  =-14


(2) -6+5-(-7)


  =(-6)+(+5)+(+7)


  =-(+6)+(5+7)


  =-6+12


  =-6


(3) 4+(-5)-7-(-2)+6


  =(+4)+(-5)+(-7)+(+2)+(+6)


  =(4+2+6)-(5+7)


  =12-12


  =0


(4) -3.5+(-1.7)-(-4.8)+2.3


  =(-3.5)+(-1.7)+(+4.8)+(+2.3)


  =-(3.5+1.7)+(4.8+2.3)


  =-5.2+7.1


  =+1.9


(5) -1/3-(-1/2)-5/6


  =(-1/3)+(+1/2)+(-5/6)


  =-(1/3+5/6)+1/2


  =-(2/6+5/6)+1/2


  =-7/6+3/6


  =-4/6


  =-2/3


(6) 3-(5-8)


  =(+3)-{(+5)-(+8)}


  =(+3)-{(+5)+(-8)}


  =(+3)-(-3)


  =(+3)+(+3)


  =+6


(7) -2-{-6-(-3)}


  =(-2)-{(-6)+(+3)}


  =(-2)-(-3)


  =(-2)+(+3)


  =1



(8) 4-{2-(3-7)}


  =(+4)-{(+2)-{(+3)-(+7)}}


  =(+4)-{(+2)-{(+3)+(-7)}}


  =(+4)-{(+2)-(-4)}


  =(+4)-{(+2)+(+4)}


  =(+4)-(+6)


  =(+4)+(-6)

  =-2


 

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