Final answer:
The director can select 4 actors from a group of 20 actors to attend the workshop in 4845 different ways.
Step-by-step explanation:
In this question, we need to find the number of different ways a director can select 4 actors from a group of 20 actors to attend a workshop on performing in rock musicals. This is a combination problem as the order of selection does not matter. To find the answer, we can use the combination formula:
Combination = nCr = n! / r!(n-r)!
Plugging in the values, we get:
Combination = 20C4 = 20! / (4! * (20-4)!) = 4845
Therefore, there are 4845 different ways a director can select 4 actors from a group of 20 actors to attend the workshop.