Answer: 1 is the greatest common factor of these numbers.
Step-by-step explanation:
5: 1, and 5.
88: 1, 2, 4, 8, 11, 22, 44, and 88
91: 1, 7, 13, and 91
There is no other common factor for 5 that matches the others. And the only numbers that factor all of these numbers provided is 1.
Hopefully this is right. Have a great day.