\(3a=4b=5c\)
\(\Rightarrow\dfrac{a}{20}=\dfrac{b}{15}=\dfrac{c}{12}\)
Áp dụng t/c dtsbn:
\(\dfrac{a}{20}=\dfrac{b}{15}=\dfrac{c}{12}=\dfrac{2a}{30}=\dfrac{a+2b-c}{20+30-12}=\dfrac{76}{38}=2\)
\(\Rightarrow\left\{{}\begin{matrix}a=20.2=40\\b=15.2=30\\c=12.2=24\end{matrix}\right.\)