To convert litres to centilitres (cl), we can use the fact that 1 litre is equal to 100 centilitres.
20 litres is equal to:
\( 20 , \text{litres} \times 100 , \text{cl/litre} = 2000 , \text{cl} \)
Now, since you want to find out how many 500 cl containers can be seen in 2000 cl, you divide:
\[ \frac{2000 , \text{cl}}{500 , \text{cl}} = 4 \]
Therefore, you can see 4 500 cl in 20 litres.