Tính nhanh:
P = \(\frac{1}{5x8}+\frac{1}{8x11}+\frac{1}{11x14}+..........+\frac{1}{602x605}\)
Q = \(\frac{4}{3x7}+\frac{5}{7x12}+\frac{1}{12x13}+\frac{7}{13x20}+\frac{3}{20x23}\)
R = \(\left(1-\frac{1}{15}\right)\times\left(1-\frac{1}{21}\right)\times\left(1-\frac{1}{28}\right)\times........\times\left(1-\frac{1}{210}\right)\)