Răspuns :
[tex]\it \{a,\ b,\ c\}\ i.\ p.\ \{2,\ 4,\ 5\}\ \Rightarrow 2a=4b=5c \Rightarrow \begin{cases} \it a=2b\\ \\ \it c=0,8b\end{cases}\\ \\ \\ 2b+b+0,8b=57 \Rightarrow 3,8b=57|_{:3,8} \Rightarrow b=15[/tex]
[tex]\it \{a,\ b,\ c\}\ i.\ p.\ \{2,\ 4,\ 5\}\ \Rightarrow 2a=4b=5c \Rightarrow \begin{cases} \it a=2b\\ \\ \it c=0,8b\end{cases}\\ \\ \\ 2b+b+0,8b=57 \Rightarrow 3,8b=57|_{:3,8} \Rightarrow b=15[/tex]