To find the joint relative frequency of elementary age students who prefer winter, we will use the formula for joint relative frequency:
\[ \text{Joint Relative Frequency} = \frac{\text{Frequency of specific group}}{\text{Total number of respondents}} \]
In this case, the frequency of elementary age students who prefer winter is \(84\), and the total number of students surveyed is \(251\).
Now we can calculate it:
\[ \text{Joint Relative Frequency} = \frac{84}{251} \]
Calculating this value gives:
\[ \frac{84}{251} \approx 0.3343 \]
To convert this into a percentage, we multiply by \(100\):
\[ 0.3343 \times 100 \approx 33.43 \]
Rounding to the nearest whole number gives us \(33\).
Therefore, the joint relative frequency of elementary age students who prefer winter is \(33\) percent.