a) (123-27)+(27+13-123)
=123-27+27+13-123
=(123-123)+(-27+27)+13
=0+0+13
=13
b) (175+25+13)-(-15+175+25)
=175+25+13-15-175-25
=(175-175)+(25-25)+(13+15)
=0+0+28
=28
c)(2012-119+29)-(-119+29)
= 2012-119+29+119-29
=2012+(119-119)+(29-29)
=2012+0
=2012
d)-(55-80+91)-(2012+80-91)
=-55+80-91-2012-80+91
=(80-80)+(91-91)-2012-55
=0-2067
=-2067
Chúc bạn học tốt! :)