Answer to Question 1
a) The decision whether to challenge the merger depends, in part, on the market's Herfindahl-Hirschman Index (HHI). The HHI for the market initially is 1,150. Thus the Department of Justice guidelines say it will challenge a merger if the merger raises the HHI by 100 or more points. If firms I and J merge, the HHI becomes 1,200. The Department of Justice will not challenge this merger.
b) If firms A and B merge, the HHI becomes 1,600. The Department of Justice will challenge this merger.
Answer to Question 2
A