Respuesta :

Using the combination formula, it is found that he can choose 126 sets of 4 materials.

The order in which the materials are chosen is not important, hence, the combination formula is used to solve this question.

Combination formula:

[tex]C_{n,x}[/tex] is the number of different combinations of x objects from a set of n elements, given by:

[tex]C_{n,x} = \frac{n!}{x!(n-x)!}[/tex]

In this problem, 4 materials are chosen from a set of 9, hence:

[tex]C_{9,4} = \frac{9!}{4!5!} = 126[/tex]

He can choose 126 sets of 4 materials.

To learn more about the combination formula, you can take a look at https://brainly.com/question/25821700

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