Answer: The probability is 1/190 = 0.005
Explanation:
The probability of ordering two specific toppings out of 20 is:
For the first selection he can order 2 of them, peperoni or sausage, so the probability for the first selection is 2/20 = 1/10 (the number of correct options divided by the total number of options)
For the second selection we have only one option, because we assume that the other one was selected previously, here we also had a total of 19 toppings because one already was selected, the probability in this selection is 1/19.
The joint probability is equal to the product of those two probabilities:
P = (1/19)*(1/10) = 1/190 = 0.005