Final answer:
The greatest common factor of 28 and 70 is 7.
Step-by-step explanation:
To find the greatest common factor (GCF) of 28 and 70, we need to find the largest number that can divide both 28 and 70 without leaving a remainder. We can start by listing the factors of each number. The factors of 28 are 1, 2, 4, 7, 14, and 28. The factors of 70 are 1, 2, 5, 7, 10, 14, 35, and 70. From this list, we can see that 7 is the largest number that can divide both 28 and 70, so the GCF of 28 and 70 is 7.