gokhale model ppr 2 doubt

[sonal dhawan]

 You have two plants. Plant A has costs c(y) = y2 and Plant B has costs c(y) = 2y2. What is the
joint cost curve?
a) y2 c) 5y2/9
b) 2y2 d) 3y

[bhavya jain]

d) just add the two cost functions to get the total..

[sonal dhawan]

heyy thanks.......bt adding the total cost curves vertically doesn't make sense conceptually....so hw can the ans be option d

[bhavya jain]

bcoz the two cost fns are in terms of both y. If they had been y1 & y2 resp, then we wud have calculated MC & equated them to find the cost fns.

[Homer Simpson]

Conceptually, we need to add them vertically because i calculate TC for a given y - therefore, TC = y^2 + 2y^2 = 3y^2