Bonjour,

a. 1 - - 7/3

= 1 + 7/3

= (1 x 3) / (1 x 3) - 7/3

= 3/3 - 7/3

= 4/3

b. - 2/3 + 7/8 - 5/6

= (- 2 x 8) / (3 x 8) + (7 x 3) / (8 x 3) - (5 x 4) / (6 x 4)

= - 16/24 + 21/24 - 20/24

= - 36/24 + 21/24

= - 15/24

= (3 x - 5) / (3 x 8)

= - 5/8

c.  - 2/10 + 7/25

= (- 2 x 5) / (10 x 5) + (7 x 2) / (25 x 2)

= - 10/50 + 14/50

= 4/50

d. 3/7 - 7/10

= (3 x 10) / (7 x 10) - (7 x 7) / (10 x 7)

= 30/70 - 49/70

= - 19/70.