Ben rolls four fair 20-sided dice, and each of the dice has faces numbered from 1 to 20. What is the probability that exactly two of the dice show an even number?
Each die will have the same probabililty of showing an even or odd number
So....the probability is
C(20,2) (1/2)^20 = 95 / 524288 ≈ .0181%
Sorry Chris but you read the question incorrectly :(
You have found the probability of rolling exactly 2 heads in 20 rolls of the dice but there are only 4 rolls.