Answer :
In this case, the order doesn't matter and the colors cant be repeated.
Now, we need to use the permutation formula:
[tex]P(n,r)=\frac{n!}{(n-r)!}[/tex]Where n represents the total different available colors and r is equal to
the number of doors.
Replacing on the permutation formula:
[tex]P(10,3)=\frac{10!}{(10-3)!}[/tex][tex]P(10,3)=\frac{10!}{7!}[/tex][tex]P(10,3)=\frac{10x9x8x7!}{7!}[/tex][tex]P(10,3)=10x9x8![/tex]Then
[tex]P(10,3)=\frac{10x9x8x7!}{7!}[/tex][tex]P(10,3)=720[/tex]Hence, there are 720 possible arrangements for the doors.