\(\dfrac{200x}{100}+\dfrac{300\left(x-20\right)}{100}=\dfrac{33.500}{100}\)
=> 200x + 300(x - 20) = 16500
<=> 200x + 300x - 6000 = 16500
<=> 500x = 22500
<=> x = 45
S = {45}
Ta có: \(\dfrac{x\cdot200}{100}+\dfrac{\left(x-20\right)\cdot300}{100}=\dfrac{33\cdot500}{100}\)
\(\Leftrightarrow200x+300x-6000=16500\)
\(\Leftrightarrow500x=22500\)
hay x=45
Vậy: S={45}