Bài 1: D
Bài 2: C
Bài 3:
a: \(21-3\dfrac{3}{4}:\left(\dfrac{3}{8}-\dfrac{1}{6}\right)=3\)
b: \(\left(2-\dfrac{3}{2}\right)\left(2-\dfrac{4}{3}\right)\left(2-\dfrac{5}{4}\right)\left(2-\dfrac{6}{5}\right)\)
\(=\dfrac{1}{2}\cdot\dfrac{2}{3}\cdot\dfrac{3}{4}\cdot\dfrac{4}{5}\)
\(=\dfrac{1}{5}\)
c: \(\dfrac{1}{2011}+\dfrac{2012\cdot2010}{2011}-2012\)
\(=\dfrac{1+2011^2-1}{2011}-2012\)
=2011-2012
=-1
d: \(\dfrac{5}{4}-\dfrac{5}{4}:\left(\dfrac{3}{8}-\dfrac{1}{6}\right)+\dfrac{11}{12}\)
\(=\dfrac{5}{4}-\dfrac{5}{4}\cdot\dfrac{24}{5}+\dfrac{11}{12}\)
\(=\dfrac{15}{12}+\dfrac{11}{12}-\dfrac{72}{12}\)
\(=-\dfrac{23}{6}\)
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