Find out the HCF of 12, 18, 24, 54

$12=2^2 \times 3$, $18=2 \times 3^2$, $24=2^3 \times 3$, $54=2 \times 3^3$; the common factors are $2 \times 3 = 6$. The value 216 is the LCM of these numbers, not the HCF, and 2 and 3 are common factors but not the highest.