-2,5-(-1 2/3+2 1/3)=

-2,5-(-1 2/3+2 1/3)= - 3 1/6.
1) -1 2 /3 + 2 1/ 3 = 2 1/ 3 - (-1 2 /3 ) = 1 + 1 /3 - 2/ 3 = 1 + 1 - 2 /3 = 1 - 1/ 3 = 1·3/ 3 - 1/ 3 = 2 /3;
2)Переводим десятичный дробь в простой -2.5= - 2 5/10 = - 2 1/2.
3) -2 1 /2 - 2 /3 = -2 - 1/ 2 - 2 /3 = -2 - 1·3/ 2·3 - 2·2/ 3·2 = -2 - 3/ 6 - 4/ 6 = -2 - 3 + 4/ 6 = -2 7 /6 = -2 1 + 1·6/ 6 = -3 1/ 6 .