LCM( 30, 20 ) = 60
The formula for finding LCM is
$$ \text{LCM} (a, b) = \frac{ a \cdot b }{ \text{GCD}(a,b)} $$In this example we have: a = 30, b = 20 and GCD(30, 20) = 10.
$$ \text{LCM} (30, 20) = \frac{ 30 \cdot 20 }{ \text{GCD}(30,20)} = \frac{ 600 }{ 10 } = 60 $$