Bonjour mon ami voilà la réponse
1) 4/5 ÷ 7/15 = 1 + 5/7
★ 4/5 ÷ 7/15 = 4/5 × 15/7
= 60/35 = 12/7 = 7/7 + 5/7 = 1 + 5/7
donc : 4/5 ÷ 7/15 = 1 + 5/7
2) 5 + 1/4 - 1 + 2/3 = 3 + 7/12
★ 5 + 1/4 + 1 - 2/3
= 60/12 + 3/12 - 12/12 + 8/12
= 63/12 - 20/12 = 43/12
= 36/12 + 7/12
= 3 + 7/12
donc 5 + 1/4 - 1 + 2/3 = 3 + 7/12