ppf and inequalities

[Eco16]

if a/b > b/c then
ac=b^2 Or no inference can be made regarding the magnitude.?


Optimal point on ppf depends on
efficiency or
preferences or
feasibility?

[Var1995]

no inference and for the second question m not clear as to what the ques is actually asking, i.e., is it asking for the conditions required to be an optimal point or is it asking for the most desirable among those optimal points. in the latter case, preferences  r gonna decide the point. m in confusion....

[Eco16]

Why no inference as b^2 will be positive and so will be ac
In second question it is asked on which factor is the optimal point selected?
I think it must be preference as every point on ppf is efficient.

[Var1995]

if a=c=b then ac=b^2
if say a=c=1 and b=-2 then ac<b^2
if say a=1, c=5 and b=2 then ac>b^2
for different choices of a, b and c, we r getting one of the above 3 relations btw ac and b^2. if nothing is said regarding the values of a,b and c in the question, then in that case we can't favor one relation over the other. i hope m making sense

[Eco16]

perfectly explained!
thank you.