13б.
Дроби.

2 3/4 - ( -1 1/2)+(-3 5/6)=??

2 3/4 - ( -1 1/2)+(-3 5/6)=2 3/4+1 1/2-3 5/6=2 3/4+1 2/4-3 5/6= 3 5/4-3 5/6= 4 1/4-3 5/6=4 3/12-3 10/12=5/12