1.
-42+75+(-14)+(-26)+56= - 42+75-14-26+56=(75+56)-(42+14+26)=131 - 82=49
12+(-20) - (-11)-(-6)-10=12-20+11+6-10=(12+11+6)-(20+10)=29-30= - 1
3 5/12 - ( -1 1/3)+( -4 3/8)=3 5/12+1 1/3 - 4 3/8=3 10/24+1 8/24 - 4 9/24=9/24=3/8
2.
-13,24+в+4,9+8,24+(-4,9)= -13,24+в+4,9+8,24 - 4,9=в - 5
при в=3 4/9
3 4/9 - 5= -(5-3 4/9)= - (4 9/9 - 3 4/9)= - 1 5/9