LCM( 40, 30 ) = 120
The formula for finding LCM is
$$ \text{LCM} (a, b) = \frac{ a \cdot b }{ \text{GCD}(a,b)} $$In this example we have: a = 40, b = 30 and GCD(40, 30) = 10.
$$ \text{LCM} (40, 30) = \frac{ 40 \cdot 30 }{ \text{GCD}(40,30)} = \frac{ 1200 }{ 10 } = 120 $$