1, Tính bằng cách rút gọn gạch chéo : a, `13/14 . 4 1/4 . 3 11/15 . 1 31/39 . 21/34 . 25/49` b, `45/62 . 2 11/14 . 49/90 . 6 1/4 . 4 12/15 . 31/91` c,

1, Tính bằng cách rút gọn gạch chéo :
a, `13/14 . 4 1/4 . 3 11/15 . 1 31/39 . 21/34 . 25/49`
b, `45/62 . 2 11/14 . 49/90 . 6 1/4 . 4 12/15 . 31/91`
c, 12 7/15 . 7 2/9 . 35/111 . 1/39 . 27/91 . 5 1/5`