2) 20 (2/5)-1 (23/30)= 20 (12/30)-1 (23/30)=19 (42/30)-1 (23/30)=18 (19/30),
3) 18 (19/30)+(13/50)=18 (95/150)+(39/150)=18 (134/150)=18 (67/75),
4) 7 (1/2)*18 (67/75)=(15/2)*((1417/75)=(1/2)*(1417/5)=1417/10,
5) 24 (2/5)-10 (23/100)=24 (40/100)-10 (23/100)=14 (17/100)=1417/100,
6) (1417/100):(1417/100)=1,
7) 11 (2/5)+1=12 (2/5).