To represent the quantity of olives to pepperonis, we first note that Francis is using 20 olives (from 1 can) and 25 pepperonis (from 1 package).
The ratio of olives to pepperonis can be written as:
\[ \text{Ratio of olives to pepperonis} = \frac{\text{Number of olives}}{\text{Number of pepperonis}} = \frac{20}{25} \]
This can also be simplified:
\[ \frac{20}{25} = \frac{4}{5} \]
Thus, the ratio of olives to pepperonis is 4:5.