Think of it like this
-2 + 1 2/3
=-2 + 1 +2/3
[ -2+1=-1 Start at -2 on the number line and go 1 unit in the positive direction that'll put you at -1 ]
=-1+2/3 Start at -1 on the number line and go 2/3 unit in the positive direction that'll put you at -1/3 ]
= -1/3