Question

tính hợp lý nếu có thể

a) \(\dfrac{1}{3}\)- \(\dfrac{2}{5}\)

b) (5\(\dfrac{2}{3}\)  - 2 ) - \(\dfrac{2}{3}\)

C) (\(\dfrac{2}{5}\) - 1 ) + ( \(\dfrac{4}{3}\) - \(\dfrac{2}{5}\))

d)   ( 1\(\dfrac{8}{9}\) + \(\dfrac{3}{4}\)) - (\(\dfrac{1}{4}\) - \(\dfrac{1}{9}\))

Answer 1

a) \(\dfrac{1}{3}-\dfrac{2}{5}\)

\(=\dfrac{5}{15}-\dfrac{6}{15}\)

\(=\dfrac{-1}{15}\)

b) \(\left(5\dfrac{2}{3}-2\right)-\dfrac{2}{3}\)

\(=\left(5+\dfrac{2}{3}-2\right)-\dfrac{2}{3}\)

\(=3+\dfrac{2}{3}-\dfrac{2}{3}\)

\(=3\)

c) \(\left(\dfrac{2}{5}-1\right)+\left(\dfrac{4}{3}-\dfrac{2}{5}\right)\)

\(=\dfrac{2}{5}-1+\dfrac{4}{3}-\dfrac{2}{5}\)

\(=\left(\dfrac{4}{3}-1\right)+\left(\dfrac{2}{5}-\dfrac{2}{5}\right)\)

\(=\dfrac{1}{3}\)

d) \(\left(1\dfrac{8}{9}+\dfrac{3}{4}\right)-\left(\dfrac{1}{4}-\dfrac{1}{9}\right)\)

\(=\left(1+\dfrac{8}{9}+\dfrac{3}{4}\right)-\left(\dfrac{1}{4}-\dfrac{1}{9}\right)\)

\(=1+\dfrac{8}{9}+\dfrac{3}{4}-\dfrac{1}{4}+\dfrac{1}{9}\)

\(=1+\left(\dfrac{8}{9}+\dfrac{1}{9}\right)+\left(\dfrac{3}{4}-\dfrac{1}{4}\right)\)

\(=1+1+\dfrac{2}{4}\)

\(=2+\dfrac{1}{2}\)

\(=\dfrac{5}{2}\)