31/2-(-21/4)+(-1/3)-1/4-(+1/6)=

问题描述:

31/2-(-21/4)+(-1/3)-1/4-(+1/6)=

=31/2+21/4-1/3-1/4-1/6
=186/12+63/12-4/12-3/12-2/12
=240/12=20