Theo đề, ta có:
\(a⋮12\) \(;\) \(a⋮25\) \(;\) \(a⋮30\) \(\Rightarrow\) \(a\in BC\left(12;25;30\right)\)
\(12\) = \(2^2.3\)
25 = \(5^2\)
30 = \(2.3.5\)
\(\Rightarrow BCNN\left(12;25;30\right)=2^2.3.5^2=300\)
\(\Rightarrow BC\left(12;25;30\right)=\left\{0;300;600;...\right\}\)
Vì 0 < a < 500
\(\Rightarrow a=300\)