Question

Tính bằng cách thuận tiện nhất: a)1678*24+77*1678-1678 b)2/5 + 4/11 + 3/5 + 18/11 + 1/4 +1/6 c) 7/9x7 + 7/9x4 - 7/9x10 e)13/7x 2/3 - 6/7 : 6/4 +14/21 g)5/9x2/6+-5/9x3/6

Answer 1

a) \(1678\cdot24+77\cdot1678-1678=1678\left(24+77-1\right)=167800\)

Answer 2

b) Ta có: \(\dfrac{2}{5}+\dfrac{4}{11}+\dfrac{3}{5}+\dfrac{18}{11}+\dfrac{1}{4}+\dfrac{1}{6}\)

\(=\left(\dfrac{2}{5}+\dfrac{3}{5}\right)+\left(\dfrac{4}{11}+\dfrac{18}{11}\right)+\dfrac{1}{4}+\dfrac{1}{6}\)

\(=3+\dfrac{1}{4}+\dfrac{1}{6}\)

\(=\dfrac{36}{12}+\dfrac{3}{12}+\dfrac{2}{12}=\dfrac{41}{12}\)

Answer 3

c) \(\dfrac{7}{9\cdot7}+\dfrac{7}{9\cdot4}-\dfrac{7}{9\cdot10}\)

\(=\dfrac{7}{9}\left(\dfrac{1}{7}+\dfrac{1}{4}-\dfrac{1}{10}\right)\)

\(=\dfrac{7}{9}\cdot\left(\dfrac{20}{140}+\dfrac{35}{140}-\dfrac{14}{140}\right)\)

\(=\dfrac{7}{9}\cdot\dfrac{41}{140}=\dfrac{41}{180}\)