How appropriate is this add on a Kids Maths web site? (plus.google.com)

Quite. I know a lot of 15-18 year old students who study maths at this level. This is, unfortunately, very relevant.

The ads are tailored to you, or whomever uses the same computer the you're are using. Google thinks you need those pills. The kids will get different ads based on what google detects as their interests.