bonjour voici les deux exercices c est pour demain merci

1) 
7/20 + 7/10 = 7/20 + 14/20 = 21/20
7/20 + 4/5 = 7/20 + 16/20 = 23/20
16/40 + 7/10 = 16/40 + 28/40 = 44/40 = 22/20
16/40 + 7/10 = 16/40 + 4/5 = 16/40 + 32/40 = 48/40 = 24/20 = 12/10 = 6/5

2) Donc, 
22/20 - 21/20 = 24/20 - 23/20
1/20 = 1/20