Đáp án:
Giải thích các bước giải
1)
x : $\dfrac{2}{5}$ = $\dfrac{4}{7}$ : $\dfrac{3}{2}$
x : $\dfrac{2}{5}$ = $\dfrac{8}{21}$
x = $\dfrac{8}{21}$ × $\dfrac{2}{5}$
x = $\dfrac{16}{105}$
2)
12 : x + $\dfrac{2}{3}$ = $\dfrac{7}{5}$
12 : x = $\dfrac{7}{5}$ - $\dfrac{2}{3}$
12 : x = $\dfrac{11}{15}$
x = 12 : $\dfrac{11}{15}$
x = $\dfrac{180}{11}$