Answer: she has 2 5/10 minutes left for question C
Explanation:
Total time that Sonya has for the three-problem quiz is 20 minutes.
She spent 10 9/10 minutes on question A. Converting 10 9/10 minutes to improper fraction, it becomes 109/10 minutes.
She spent 6 3/5 minutes on question B. Converting 6 3/5 minutes to improper fraction, it becomes 33/5 minutes.
Total time spent on question A and question B is
109/10 + 33/5 = (109 + 66)/10
= 175/10 minutes
The amount of time that she has left for question C would be
20 - 175/10 = (200 - 175)/10
= 25/10 = 2 5/10 minutes