You may want to teach your brother how to guess, because a solid educated guess is also an opportunity for you to assess his level of understanding. A student

You may want to teach your brother how to guess, because a solid educated guess is also an opportunity for you to assess his level of understanding. A student guess is an opportunity for you to learn what they understand and what they still need help with. If a student makes an attempt on a well-written multiple choice test, the attempt can show the teacher exactly what the student does and doesn't understand. The right approach to guessing can communicate a lot, and partial credit may be justified if, for example, the student correctly factors a quadratic equation but fails to remember how to compute the intercepts from the result. That would tell a teacher that the student remembers part of the lesson but needs help with the rest.