(-12)+11+(-8)+(+39)=?

问题描述:

(-12)+11+(-8)+(+39)=?

(-12)+11+(-8)+(+39)
=-12+11-8+39
=39+11-12-8
=50-20
=30

=(-1)+(-8)+(+39)=(-7)+(+39)=32

(-12)+11+(-8)+39
=-1+(-8)+39
=-9+39
=30

=-12+11-8+39
=(11+39)-(12+8)
=50-20
=30

(-12)+11+(-8)+(+39)
=-12+11-8+39
=-(12+8)+(11+39)
=-20+50
=30