Bonjour

73)

a. 5/12 - 5/3 + 1/6 - 2/9

= (5 x 3) / (12 x 3) - (5 x 12) / (3 x 12) + (1 x 6) / (6 x 6) - (2 x 4) / (9 x 4)

= 15/36 - 60/36 + 6/36 - 8/36

= 47/36

b. 3/7 + 3/4 - 5/2 - 17/8

= (3 x 8) / (7 x 8) + (3 x 14) / (4 x 14) - (5 x 28) / (2 x 28) - (17 x 7) / (8 x 7)

= 24/56 + 42/56 - 140/56 - 119/56

= - 193/56

74)

a. 2 - 1/3 + 1/6 - 1/9

= (2 x 18) / (1 x 18) + (1 x 3) / (6 x 3) - (1 x 2) / (9 x 2)

= 36/18 + 3/18 - 2/18

= 37/18

b. 1 + 1/2 + 3/4 + 5/6

= (1 x 12) / (1 x 12) + (1 x 6) / (2 x 6) + (3 x 3) / (4 x 3) + (5 x 2) / (6 x 2)

= 12/12 + 6/12 + 9/12 + 10/12

= 37/12

75)

a. 4/3 - (1/2 + 7/8)

= (4 x 8) / (3 x 8) - [(1 x 12) / (2 x 12) + (7 x 3) / (8 x 3)]

= 32/24 - (12/24 + 21/24)

= 32/24 - 33/24

= - 1/24.

b. 4/3 - 7/5 + (3/5 - 5/7)

= (4 x 35) / (3 x 35) - (7 x 21) / (5 x 21) + [(3 x 21) / (5 x 21) - (5 x 15) / (7 x 15)]

= 140/105 - 147/105 + (63/105 - 75/105)

= - 7/105 - 12/105

= - 19/105.