Final answer:
There are 126 different ways to select 4 toppings for a pizza from 9 different toppings, without repeating any toppings.
Step-by-step explanation:
When selecting 4 toppings for a pizza from a choice of 9 different toppings, we need to determine whether we should use permutations or combinations. In this case, order does not matter and toppings cannot be repeated, so we will use combinations.
Using the formula for combinations, which is nCr = n!/((n-r)!r!), we can calculate the number of ways to select 4 toppings from 9. Plugging in the values, we get 9!/((9-4)!4!) = 9!/(5!4!) = 9x8x7x6/(4x3x2x1) = 126.
Therefore, there are 126 different ways to select 4 toppings for a pizza from 9 different toppings, without repeating any toppings.