To determine the mode or modes of the ages in the provided data set, we need to identify which age(s) appear most frequently.
Based on the survey results:
- 14 years old: 15%
- 15 years old: 50%
- 16 years old: 20%
- 17 years old: 15%
The age that has the highest percentage of respondents is 15 years old (50%). Since 15 years old is the only age that appears with the highest frequency, the mode of this data set is:
15