Find the ratio between the LCM and HCF of 5, 15, and 20.

By prime factorisation:

5= 5 x 1
15 = 5 × 3
20 = 2 × 2 × 5
 

Least Common Multiple of (5, 15, 20) = 5 × 3 × 2 × 2 = 60
Highest Common Factor of (5, 15, 20) = 5

$\mathrm{Ratio}=\frac{\mathrm{LCM}}{\mathrm{HCF}}=\frac{60}{5}=\frac{12}{1}=12:1$

Therefore, 12:1 is the correct ratio.