2 per 5 + 2 per 7 - 3 per 2 Pliss sama caranya

2/5 + 2/7 - 3/2
= 28/70 + 20/70 - 105/70
= 48/70 - 105/70
= -57/70

2/5 + 2/7 - 3/2

pertama kerjakan 
2/5 + 2/7 = 14+10/35 = 24/35

24/35-3/2
= 48-105/70
=-57/70