Thực hiện phép tính(Tính nhanh nếu có thể):
a) 0,25.\(\dfrac{12}{5}\).\(\dfrac{100}{7}\).49%
b)\(\dfrac{3}{8}\)+0,125.\(\dfrac{3}{4}\)-\(1\dfrac{1}{4}\)
c)\(\dfrac{-13}{27}\).\(\dfrac{4}{9}\)+\(\dfrac{4}{9}\).\(\dfrac{-14}{27}\)-\(\dfrac{5}{9}\)
d)\(\dfrac{2}{3.7}\)+\(\dfrac{2}{7.11}\)+\(\dfrac{2}{11.15}\)+.....+\(\dfrac{2}{91.95}\)
a: \(=\dfrac{1}{4}\cdot\dfrac{12}{5}\cdot\dfrac{100}{7}\cdot\dfrac{49}{100}\)
\(=\dfrac{1}{4}\cdot\dfrac{12}{5}\cdot\dfrac{49}{7}=\dfrac{3}{5}\cdot7=\dfrac{21}{5}\)
b: \(=\dfrac{3}{8}+\dfrac{1}{8}\cdot\dfrac{3}{4}-\dfrac{5}{4}\)
\(=\dfrac{12}{32}+\dfrac{3}{32}-\dfrac{40}{32}=\dfrac{-25}{32}\)
c: \(=\dfrac{4}{9}\left(\dfrac{-13}{27}-\dfrac{14}{27}\right)-\dfrac{5}{9}=\dfrac{-4}{9}-\dfrac{5}{9}=-1\)
d: \(=\dfrac{2}{4}\left(\dfrac{4}{3\cdot7}+\dfrac{4}{7\cdot11}+...+\dfrac{4}{91\cdot95}\right)\)
\(=\dfrac{1}{2}\left(\dfrac{1}{3}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{11}+...+\dfrac{1}{91}-\dfrac{1}{95}\right)\)
\(=\dfrac{1}{2}\cdot\dfrac{92}{285}=\dfrac{46}{285}\)
