[alisonkisk]

I didn't see that in the document. What page is it on?

[OJFord]

I think they mean at the bottom of p216 (pdf page 4), where he says he doesn't know, r+s=80 but there isn't enough information to solve for r and s.

[impossiblefork]

There's two questions that are intended to be wrong (probably to test confidence). One with insufficient information and where the question itself implies falsehoods.

[impossiblefork]

The questions are on page 215 (3/26) and Tao's answers are on the next page.