Giải thích các bước giải:
a.Ta có:
$\dfrac7{15}\cdot \dfrac53+\dfrac8{15}\cdot\dfrac53$
$=\dfrac53\cdot (\dfrac7{15}+\dfrac8{15})$
$=\dfrac53\cdot 1$
$=\dfrac53$
b.Ta có:
$\dfrac34+\sqrt{\dfrac{16}{25}}+ (\dfrac{-1}{2})^2$
$=\dfrac34+\sqrt{(\dfrac35)^2}+\dfrac14$
$=\dfrac34+\dfrac35+\dfrac14$
$=(\dfrac34+\dfrac14)+\dfrac35$
$=1+\dfrac35$
$=\dfrac85$
c.Ta có:
$(\dfrac25-1)^2:|\dfrac{-2}{5}|$
$=(-\dfrac35)^2:\dfrac25$
$=\dfrac{9}{25}\cdot\dfrac52$
$=\dfrac9{10}$
