You need to use the division ladder to evaluate the greatest common factor of the numbers 10 and 15, hence, you need to find the prime factors of 10 and 15.

Notice that 5 is a common prime factor of 10 and 15, hence, you need to divide by 5 the numbers 10 and 15, such that:

`10/5 = 2`

`15/5 = 3`

You need to search the commoon factors of the results 2 and 3 and there exists no common factor.

**Hence, evaluating the greatest common factor (GCF) of the numbers 10 and 15, yields `GCF = 5.` **

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**Further Reading**