Explain 15 is not a prime factor

15 is not a prime factor as it is divided by 1,3,5 and 15.

Additional information:

Prime numbers are those numbers which can only be divided by itself .for instance:1,2,3,5,7 ,11,13 etc.

Composite number s are those numbers which can be also divided by other numbers,For instance: 4,6,8,10 etc

Hope it helps

there is only one way to arrange all the eight relative to each other because they are not distinct. we have

now there are nine places to place an (and not more than one in one place).   because we have four symbols, we need to choose four of these nine places to insert an . order does not matter because the are not distinct.

thus there are 1 · c(9,4) ways, or, if we calculate it,

thus there are 126 ways to form such "words."