(1) 8＋(-9)＋2＋(-1) = (8+2)＋[(-9)+(-1)] = 10+(-10) = 0
(2) (-7)＋4＋(-3)＋(-4) = (-7) + [4+(-4)] +( -3) = (-7)+(-3) = -10
(3) 3.47＋(-2.7)＋(-3.47)＋(-2.3) = [3.47+(-3.47)] + [(-2.7)+(-2.3)] = 0+(-5) = -5
(4) (-1又7分之1)＋5 = -1又7分之1 + 4又7分之7 = 3又7分之6（-1又7分之1）＋5分之3＋7分之4加（-5分之1）(-1又7分之1) + 5分之3 + 7分之4 + (-5分之1)= [5分之3+(-5分之1)] + (-1又7分之1 + 7分之4)=2/5 - 4/7=14/35 - 20/35= -6/35