7 : 7 1/2 - (5 1/15 * 3 - 12 19/30) : 2,75 = 0
1. 7 : 7 1/2 = 7 : 15/2 = 7 * 2/15 = 14/15
2. 5 1/15 * 3 = 15 1/5
3. 15 1/5 - 12 19/30 = 14 36/30 - 12 19/30 = 2 17/30
4. 2 17/30 : 2,75 = 77/30 : 275/100 = 77/30 * 100/275 = 770/825 = 14/15
5. 14/15 - 14/15 = 0