=7.2-3.6+3.6+2.5
=(7.2+2.5)+(-3.6+3.6)
=9.7+0
=9.7
2、(-72)-(-37)-(-22)-17
=-72+37+22-17
=(-72+22)+(37-17)
=-50+20
=-30
3、0-(+3)-|-3.5|-(-4.2)
=0-3-3.5+4.2
=-3-3.5+4.2
=-6.5+4.2
=-2.3
4、1/2-(-1/2)-(-3/4)-1/6
=1/2+1/2+3/4-1/6
=1+3/4-1/6
=7/4-1/6
=21/12-2/12
=19/12
=1又7/12
5、2/3-1/8-(-1/3)+(-3/8)
=2/3-1/8+1/3-3/8
=(2/3+1/3)-(1/8+3/8)
=1-1/2
=1/2