Final answer:
The rhetorical device used in the student's statement is pathos, which appeals to the audience's sense of fairness and moral duty.
Step-by-step explanation:
The rhetorical device used in the statement 'Since my little brother has to start school before me, I should let him use the bathroom first' is pathos. This appeals to the reader's sense of fairness and responsibility. The speaker is suggesting that it is only right to allow their younger sibling to prepare for school first due to the earlier start time, thereby invoking a sense of moral duty in the audience. Pathos often aims to elicit an emotional response, and in this case, the statement is appealing to the audience's sense of empathy and compassion.