\(\dfrac{3}{x+5}=\dfrac{3}{20}\Rightarrow3.\left(x+5\right)=3.20\Rightarrow3x+15=60\Rightarrow3x=45\Rightarrow x=15\)vậy x=15
Có: \(15\%=0,15=\dfrac{15}{100}=\dfrac{3}{20}\)
Mà 15% = \(\dfrac{3}{x+5}\)
=> \(\dfrac{3}{x+5}=\dfrac{3}{20}\)
=> x+5 = 20
=> x= 15
Vậy x = 15