Question

Tính giá trị biểu thức.

a) \(\dfrac{4}{9}+\dfrac{2}{9}-\dfrac{5}{18}\)                   b) \(2-\dfrac{3}{5}+\dfrac{8}{15}\)                       c) \(\dfrac{9}{8}-\left(\dfrac{11}{8}-\dfrac{19}{32}\right)\)

Answer 1

a)

\(\dfrac{4}{9}+\dfrac{2}{9}-\dfrac{5}{18}\\ =\dfrac{6}{9}-\dfrac{5}{18}\\ =\dfrac{6\times2}{9\times2}-\dfrac{5}{18}\\ =\dfrac{12}{18}-\dfrac{5}{18}\\ =\dfrac{7}{18}\)

b)

\(2-\dfrac{3}{5}+\dfrac{8}{15}\\ =\dfrac{2\times15}{15}-\dfrac{3\times3}{5\times3}+\dfrac{8}{15}\\ =\dfrac{30-9+8}{15}\\ =\dfrac{29}{15}\)

c)

\(\dfrac{9}{8}-\left(\dfrac{11}{8}-\dfrac{19}{32}\right)\\ =\dfrac{9}{8}-\left(\dfrac{11\times4}{8\times4}-\dfrac{19}{32}\right)\\ =\dfrac{9}{8}-\left(\dfrac{44}{32}-\dfrac{19}{32}\right)\\ =\dfrac{9}{8}-\dfrac{25}{32}\\ =\dfrac{9\times4}{8\times4}-\dfrac{25}{32}\\ =\dfrac{36-25}{32}\\ =\dfrac{11}{32}\)

Answer 2

a) \(\dfrac{4}{9}+\dfrac{2}{9}-\dfrac{5}{18}=\dfrac{8}{18}+\dfrac{4}{18}-\dfrac{5}{18}=\dfrac{8+4-5}{18}=\dfrac{7}{18}\)

b) \(2-\dfrac{3}{5}+\dfrac{8}{15}=\dfrac{30}{15}-\dfrac{9}{15}+\dfrac{8}{15}=\dfrac{30-9+8}{15}=\dfrac{29}{15}\)

c) \(\dfrac{9}{8}-\left(\dfrac{11}{8}-\dfrac{19}{32}\right)=9-\left(\dfrac{44}{32}-\dfrac{19}{32}\right)=9-\dfrac{25}{32}=\dfrac{288}{32}-\dfrac{25}{32}=\dfrac{288-25}{32}=\dfrac{263}{32}\)