Tính :

Tính :
B = 1/7 . 1/5 + 1/7 . 2/5 + 1/7 . 4/5
C = 8/19 . 5/11 + 7/11 . 8/19 - 1/11 . 8/19
D = 5.18-20.27+15.36 / 10.36-20.54+30.72
E= 4/9 . (-1/19) + 5/9 . (-7/19)