∵|a-1|+|b+2|+|1-3c|=0,
∴|a-1|=0,|b+2|=0,|1-3c|=0.
a=1,b=-2,c=1/3
∴abc÷(a+b-c)
=1×(-2)×(1/3)÷(1-2-1/3)
=(-2/3)÷(-4/3)
=½