This document last updated: 30 May 2018.
I'll list corrections to the main pdf document here and incorporate them into the pdf document at the end of an academic year.
2015 A2 (a)(iv): should just be d < b as question says b and d are positive.
2015 B5 (a): should be <= not <, since we require only weak concavity not strict concavity.
2017 A1 (b)(ii) there is no gamma in the answer