To find the relative frequency of the people age 12–15 who had over 500 messages, we first need to calculate the total number of people age 12–15 and then determine how many of those sent over 500 messages.
From the table, the number of text messages for the age group 12–15 is:
- 0–200 messages: 24
- 201–500 messages: 47
- Over 500 messages: 78
Now, we calculate the total number of people in the age group 12–15:
\[ \text{Total for age 12–15} = 24 + 47 + 78 = 149 \]
Next, we find the number of people age 12–15 who sent over 500 messages, which is 78.
Now, we calculate the relative frequency for the age group 12–15 who had over 500 messages:
\[ \text{Relative frequency} = \frac{\text{Number of people with over 500 messages}}{\text{Total number of people}} = \frac{78}{149} \]
Now we calculate the percentage:
\[ \text{Relative frequency (in percentage)} = \left(\frac{78}{149}\right) \times 100 \approx 52.34% \]
Rounding to the nearest tenth, the relative frequency of people age 12–15 who had over 500 messages is:
\[ \boxed{52.3%} \]