Question

[Dáng Nguyễn]

Thực hiện phép tính ( tính nhanh nếu có thể ) 

a , \(\dfrac{-2}{9}\)+ \(\dfrac{8}{15}\)+\(1\dfrac{2}{3}\)- \(\dfrac{7}{9}\)+ \(\dfrac{-7}{-15}\)                   b , \(\dfrac{2}{7}\). \(10\dfrac{2}{8}\)- \(\dfrac{2}{7}\). \(3\dfrac{1}{4}\)

c, \(\dfrac{5}{7}\)+ \(\dfrac{2}{7}\): 0,25 - 0,4

Answer 1

[Nguyễn Lê Phước Thịnh]

a: \(\dfrac{-2}{9}+\dfrac{8}{15}+1\dfrac{2}{3}-\dfrac{7}{9}+\dfrac{-7}{-15}\)

\(=\left(-\dfrac{2}{9}-\dfrac{7}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)+\dfrac{5}{3}\)

\(=-1+1+\dfrac{5}{3}=\dfrac{5}{3}\)

b: \(\dfrac{2}{7}\cdot10\dfrac{2}{8}-\dfrac{2}{7}\cdot3\dfrac{1}{4}\)

\(=\dfrac{2}{7}\left(10+\dfrac{1}{4}-3-\dfrac{1}{4}\right)\)

\(=\dfrac{2}{7}\cdot7=2\)

c: \(\dfrac{5}{7}+\dfrac{2}{7}:0,25-0,4\)

\(=\dfrac{5}{7}+\dfrac{2}{7}\cdot4-\dfrac{2}{5}\)

\(=\dfrac{5}{7}+\dfrac{8}{7}-\dfrac{2}{5}=\dfrac{13}{7}-\dfrac{2}{5}=\dfrac{65-14}{35}=\dfrac{51}{35}\)