$\dfrac {1} {2}:\dfrac {1} {3}:\dfrac {1} {4}$
$=\left( \dfrac {1} {2}\times 12\right) :\left( \dfrac {1} {3}\times 12\right) :\left( \dfrac {1} {4}\times 12\right)$
(12 is the lowest common multiple of 2, 3, and 4)
$=6:4:3$
Meaning of Lowest Common Multiple
It's a lowest quantity that is a multiple of two or more given quantities.
(Source: Yahoo answer, Google)
