Răspuns:
a) 5/12 - 3/14 + 2/7 =
= 70/168 - 36/168 + 2/7 =
= 34/168 + 2/7 =
= 34/168 + 48/168 =
= 82/168 (simplificăm cu 2) = 41/84
b) 9/20 + 7/10 - 2/5 =
= 9/20 + 14/20 - 2/5 =
= 23/20 - 2/5 =
= 23/20 - 8/20 =
= 15/20 (simplificăm cu 5) = 3/4
c) 11/20 - (1/4 + 1/5) =
= 11/20 - (5/20 + 4/20) =
= 11/20 - 9/20 =
= 2/20 (simplificăm cu 2) = 1/10