a: x/15=7/5
nên \(x=\dfrac{7}{5}\cdot15=21\)
b: \(\dfrac{14}{x}=\dfrac{7}{5}\)
nên \(x=14\cdot\dfrac{5}{7}=10\)
c: \(\dfrac{2}{3}:\dfrac{1}{3}x=\dfrac{7}{5}:\dfrac{4}{5}=\dfrac{7}{5}\cdot\dfrac{5}{4}=\dfrac{7}{4}\)
=>1/3x=2/3:7/4=2/3x4/7=8/21
=>x=8/21:1/3=8/21x3=8/7