1/3-2/9, 3/20+5/8, 7/18+1/6-0,2 Помогите пожалуйста!!!

1) ( 1/3 ) - ( 2/9 ) = ( 3/9 ) - ( 2/9 ) = 1/9 ;
2) ( 3/20 ) + ( 5/8 ) = ( 6/40 ) + ( 25/40 ) = 31/40 ;
3) ( 7/18 ) + ( 1/6 ) - 0,2 = ( 7/18 ) + ( 3/18 ) - ( 2/10 ) = ( 10/18 ) - ( 2/10 ) =
    = ( 5/9 ) - ( 1/5 ) = ( 25/45 ) - ( 9/45 ) = 16/45 

1/3-2/9=3/9-2/9=1/9
3/20+5/8=6/40+25/40=31/40
7/18+1/6-0.2=7/18+3/18-0.2=10/18-0.2=0,05

последний пример неверный (( 10/18 = 0,5555......