The maths with the fake/real cocaine bags doesn't add up. Although we are not informed how many bags are fake, we know six are real. It is stated that Brooke has a "6:30 chance of getting away with it - 1 in 5". A 6:30 chance is 1 in 6. Conversely a "1 in 5" chance would require 24 fake bags, not 30.
Further, if the 1st and 4th bags are checked 2/3 of the time, and those will be real, Brooke has at least a 67% chance of success. Even if ALL the rest were fake, this chance can't ever fall to "1 in 4" as is stated, unless more than two bags are checked, which we are not told.