Ответ:

Пошаговое объяснение:

21/30+3/30-8/30=(21+3-8)/30=16/30=8/15;

31/200 - (35/200-19/200)=31/200 - ((35-19)/200) = 31/200 - 16/200 = 15/200=

=3/40;

21/65 - 16/65 + 13/65= (21-16+13)/65=18/65;

21/30 - (1/30 + 9/30) = 21/30 - ((1+9)/30) = 21/30 -10/30=11/30;

17/19 - (5/19+2/19) = 17/19 - ((5+2)/19)= 17/19 - 7/19 = 10/19;

3/10+5/10-7/10=(3+5-7)/10 = 1/10.