Answer:
12.5
Step-by-step explanation:
13.5 12.5 10.8 9 11 10 12.5 13 10.5 12
The mode is the number that appears the most number of times.
We place the numbers in ascending order just for convenience.
9 10 10.5 10.8 11 12 12.5 12.5 13 13.5
Every number appears once except 12.5 that appears twice.
Answer: 12.5