Kym's explanation is incorrect because the ratio of boys to girls being 25:25 means that there is an equal number of boys and girls, not that boys make up 25% of the total students.
In a ratio of 25:25, we interpret that there are 25 boys and 25 girls. This means that the total number of students in the cafeteria is 25 + 25 = 50 students.
To find the percentage of boys, we can use the formula:
\[ \text{Percentage of boys} = \left(\frac{\text{Number of boys}}{\text{Total number of students}}\right) \times 100 \]
Substituting in the numbers:
\[ \text{Percentage of boys} = \left(\frac{25}{50}\right) \times 100 = 50% \]
Thus, Kym's statement that 25% of the students were boys is incorrect; in fact, 50% of the students were boys.