Question

tính bằng cách hợp lí

a) \(\dfrac{2}{5}\) + \(\dfrac{2}{3}\) + \(\dfrac{2}{5}\)

b) \(\dfrac{6}{7}\) - \(\dfrac{5}{14}\) - \(\dfrac{3}{7}\)

c) (\(\dfrac{2}{5}\) + \(\dfrac{3}{5}\)) ✖ \(\dfrac{5}{3}\)

d) 1 : \(\dfrac{5}{6}\) - 1

Answer 1

a: =4/5+2/3=12/15+10/15=22/15

b: =3/7-5/14=1/14

c: =1*5/3=5/3

d: =6/5-1=1/5

Answer 2

\(a)\dfrac{2}{5}+\dfrac{2}{3}+\dfrac{2}{5}=(\dfrac{2}{5}+\dfrac{2}{5})+\dfrac{2}{3}=\dfrac{4}{5}+\dfrac{2}{3}=\dfrac{22}{15}\)

\(b)\dfrac{6}{7}-\dfrac{5}{14}-\dfrac{3}{7}=(\dfrac{6}{7}-\dfrac{3}{7})-\dfrac{5}{14}=\dfrac{3}{7}-\dfrac{5}{14}=\dfrac{1}{14}\)

\(c)(\dfrac{2}{5}+\dfrac{3}{5}).\dfrac{5}{3}=1.\dfrac{5}{3}=\dfrac{5}{3}\)

\(d)1:\dfrac{5}{6}-1=\dfrac{6}{5}-1=\dfrac{1}{5}\)