(a) Calculate the following: \( \begin{array}{lll}\text { (1) } \frac{1}{2} \times \frac{1}{2} & \text { (2) } \frac{3}{5} \times \frac{3}{4} & \text { (3) } \frac{2}{5} \times-\frac{3}{7} \\ \text { (4) } \frac{-1}{3} \times \frac{1}{3} \times \frac{1}{-3} & \text { (5) } \frac{1}{2} \times \frac{1}{3} \times \frac{1}{5} & \text { (6) }-\frac{2}{7} \times-3 \times-\frac{1}{4} \\ \text { (7) } \frac{3}{4} \times 4 & \text { (8) } \frac{7}{15} \times-15 & \text { (9) } 234 \times \frac{711}{-234} \\ \text { (10) } \frac{3}{4} \times \frac{8}{9} & \text { (11) } \frac{7}{15} \times \frac{10}{21} & \text { (12) }-\frac{5}{9} \times \frac{9}{20} \\ \text { (13) } \frac{3}{4} \times \frac{4}{3} & \text { (17) }\left(\frac{-1}{2}\right)\left(\frac{-1}{3}\right)\left(\frac{-1}{5}\right) & \left.\text { (18) } \frac{5}{2} \times \frac{1}{2}\right)\left(\frac{2}{3}\right)\left(\frac{3}{4}\right)\left(\frac{4}{5}\right)\left(\frac{5}{6}\right)\end{array} \)

(1) \( \frac{1}{2} \times \frac{1}{2} = \frac{1}{4} \) (2) \( \frac{3}{5} \times \frac{3}{4} = \frac{9}{20} \) (3) \( \frac{2}{5} \times -\frac{3}{7} = -\frac{6}{35} \) (4) \( \frac{-1}{3} \times \frac{1}{3} \times \frac{1}{-3} = \frac{1}{27} \) (5) \( \frac{1}{2} \times \frac{1}{3} \times \frac{1}{5} = \frac{1}{30} \) (6) \( -\frac{2}{7} \times -3 \times -\frac{1}{4} = \frac{3}{14} \) (7) \( \frac{3}{4} \times 4 = 3 \) (8) \( \frac{7}{15} \times -15 = -7 \) (9) \( 234 \times \frac{711}{-234} = -711 \) (10) \( \frac{3}{4} \times \frac{8}{9} = \frac{2}{3} \) (11) \( \frac{7}{15} \times \frac{10}{21} = \frac{1}{9} \) (12) \( -\frac{5}{9} \times \frac{9}{20} = -\frac{1}{4} \) (13) \( \frac{3}{4} \times \frac{4}{3} = 1 \) (17) \( \left(\frac{-1}{2}\right)\left(\frac{-1}{3}\right)\left(\frac{-1}{5}\right) = -\frac{1}{30} \) (18) \( \left(\frac{5}{2} \times \frac{1}{2}\right)\left(\frac{2}{3}\right)\left(\frac{3}{4}\right)\left(\frac{4}{5}\right)\left(\frac{5}{6}\right) = \frac{1}{3} \)