Answer:
125,970
Explanation:
Even if jury are assigned numbers, the order in which they are picked has no importance. That means that it's a combination, not a permutation.
The formula to calculate possible combinations is:

Where n is the global population, and r is the number of selected items.
In our case, n = 20 and r = 12, so...

There are 125970 different ways to select 12 jury members out of 20 people.