4) Calcule: a) (8)/(13)-(5)/(13) b) (7)/(8)-(1)/(4) c) (8)/(9)-(3)/(5) d) (9)/(10)-(7)/(3) e) (13)/(18)-(7)/(12) f) (3)/(4)-(2)/(5)+(6)/(7)

Vamos calcular cada uma das expressões:<br /><br />a) $\frac {8}{13}-\frac {5}{13} = \frac {8-5}{13} = \frac {3}{13}$<br /><br />b) $\frac {7}{8}-\frac {1}{4} = \frac {7}{8}-\frac {2}{8} = \frac {7-2}{8} = \frac {5}{8}$<br /><br />c) $\frac {8}{9}-\frac {3}{5} = \frac {40}{45}-\frac {27}{45} = \frac {40-27}{45} = \frac {13}{45}$<br /><br />d) $\frac {9}{10}-\frac {7}{3} = \frac {27}{30}-\frac {70}{30} = \frac {27-70}{30} = -\frac {43}{30}$<br /><br />e) $\frac {13}{18}-\frac {7}{12} = \frac {26}{36}-\frac {21}{36} = \frac {26-21}{36} = \frac {5}{36}$<br /><br />f) $\frac {3}{4}-\frac {2}{5}+\frac {6}{7} = \frac {15}{20}-\frac {8}{20}+\frac {24}{28} = \frac {15-8}{20}+\frac {24}{28} = \frac {7}{20}+\frac {24}{28} = \frac {7}{20}+\frac {6}{7} = \frac {49}{140}+\frac {120}{140} = \frac {169}{140} = 1.21$