1) 3 - ( 2/11 ) = 2 ( 11/11 ) - ( 2/11 ) = 2 ( 9/11 )
2) 2 ( 9/11 ) : 5 ( 1/6 ) = ( 31/11 ) : ( 31/6 ) = 6/11
3) 20 ( 2/3 ) + ( 6/11 ) = 20 ( 22/33 ) + ( 18/33 ) = 20 ( 40/33 ) = 21 ( 7/33 )
4) 21 ( 7/33 ) - 7,5 = 21 ( 7/33 ) - 7 ( 1/2 ) = 21 ( 14/66 ) - 7 ( 33/66 ) = 20 ( 80/66 ) - 7 ( 33/66 ) = 13 ( 47/66 )