А)-3/7+2/3=б)2/9+(-5/9))+2/3в)(0,8+(-1/6))+(-2 1/3)=

Найдем значения выражений:

А) -3/7 + 2/3 = (-3 * 3 + 2 * 7)/21 = (-9 + 14)/21 = (14 - 9)/21 = 5/21;

б) 2/9 + (-5/9) + 2/3 = 2/9 - 5/9 + 2/3 = (2 * 1 - 5 * 1 + 2 * 3)/9 = (2 - 5 + 6)/9 = (-3 + 6)/9 = 3/9 = 1/3; 

в) (0,8 + (-1/6)) + (-2 1/3) = 0.8 - 1/6 - 2 1/3 = 8/10 - 1/6 - 7/3 = 4/5 - 1/6 - 7/3 = (4 * 6 - 1 * 5 - 7 * 10)/30 = (24 - 5 - 70)/30 = (19 - 70)/30 = -79/30 = -2 19/30.