The answer is 1/100.
To calculate this, a multiplication rule is used. The multiplication rule calculates the probability that both of two events will occur. In this method, the possibilities of each event are multiplied.
There are in total 10 different toppings (1 of them is pepperoni and 1 of them is sausage) and we have 2 events occurring together:
1. the probability (P1) that you end up with pepperoni: P1 = 1/10
2. the probability (P2) that you end up with sausage: P2 = 1/10
Now, using the multiplication rule, the probability (P) that you end up with pepperoni and sausage is 1/100:
P = P1 · P2 = 1/10 · 1/10 = 1/100