How many 12 member juries can be chosen from a pool of 40 people

Since order does not matter you need to use the "n choose k" formula to find the number of unique combinations.

n!/(k!(n-k)!)  where n is the total number of possible choices and k is the number of choices made.

In this case we have:

40!/(12!(40-12)!)=5,586,853,480