Tỉnh nhanh

Tỉnh nhanh
a) 5/19.8/19+14/19.8/19+11/19
b) 3/19.7/5-3/19.2/5+2/3
c) 3/11.19/12+15/38+3/11.7/12+23/38
d) (3/4+3/5+3/7-3/11) :(6/4+6/5+6/7-6/11)