Bài 2 Tính nhanh
a) \(\dfrac{5}{23}\) x \(\dfrac{17}{26}\) + \(\dfrac{5}{23}\) x \(\dfrac{10}{26}\) - \(\dfrac{5}{23}\)
b) \(\dfrac{1}{7}\) x \(\dfrac{5}{9}\) + \(\dfrac{5}{9}\) x \(\dfrac{2}{7}\) + \(\dfrac{5}{9}\) x \(\dfrac{1}{7}\) + \(\dfrac{5}{9}\) x \(\dfrac{3}{7}\)