What made this question hard for the student? How come they got it wrong? Why did the student get it wrong in this particular way?

Today’s submission comes from Tina Cardone, who blogs at Drawing On Math.

  • Preservice teachers took a go at this:
    student knows Pythagorean identity, but misapplies it.
    They believe the student cheated, mistaking 159 for 156, and then backwards reasoned to get values. They were totally mystified by sqrt(90)=6.05 and sqrt(180)=6.59.
    They used trig to get the answer, not being too familiar with 30-60-90 triangles.