Tính bằng cách thuận tiện nhất:

a) 60 x (\(\dfrac{7}{12}\) + \(\dfrac{4}{15}\))

b) \(\dfrac{1}{2}\) x \(\dfrac{2}{3}\) x \(\dfrac{3}{4}\) x \(\dfrac{4}{5}\) x \(\dfrac{5}{6}\) x \(\dfrac{6}{7}\) x \(\dfrac{7}{8}\) x \(\dfrac{8}{9}\)

2/3