ANSWER:
11
EXPLANATION:
The greatest common factor of numbers can be said to be the greatest number which divides the numbers without leaving any remainder.
Let's first find the factors of 11 and 55
Factors of 11 = 1, and 11
Factors of 55 = 1, 5, 11, and 55
We can see there are 2 common factors of 11 and 55 which are: 1 and 11
Therefore the greatest common factor is 11
