DSE 2009 and 2011 contradiction

[ritu]

friends ,
in dse 2009,question 43....
we have the situation M=100,pa=10,pb=20.......bundle chosen is (4,3)
now when M=100,pa=20,pb=20.......bundle chosen is (5,0)
inference:since as pa rises quantity of a rises so a is a giffen good in relevant price range.....it follows that it is an inferior good as well.....
i dont understand the case of complements,,,,,as far as i know for complements we have dx/dp <0...as price of one gud rises ,quantity of its complement falls ...this is satisfied in this question but problem is quantity of b falls to zero which in my view then shudnt be a complement coz being complementry means a nd b have to be consumed together.....NOT THAT QTY OF ONE GOOD FALLS TO 0
answer key says its just giffen and inferior to which i completely agree......


again in dse 2011,exactly same question came with options:
a.a is inferior
b.b is complement of a
c.a is giffen
d,all of the above


in my view answer shud be c.a is giffen coz it includes the case of option a .....but key says its d)all of above.....same question but answers are different...


:((((((((((
.PLS CLARIFY.

[ritu]

dse 2009
27.a function f(x1,x2,T)=(y1,y2) is defined as follows,where x1,x2,t are non-negative real nos and x1+x2>=T.also for real no a,
y1=min(a,x1)   and   y2=min(a,x2) such that y1+y2=T.find f(5,2,6)
a.(3,3)
b.(5,1)
c.(0,6)
d.(4,2)


what is this question all abt..????

[rahul]

y1+ y2=6
(a, 5)+ min(a,2)=6
so possible value of "a " will be in in between 2 & 5
so use a=3
then 3+2<6
now a=4,
4+2=6 satisfy the condition
hence (4,2)

[Amit Goyal]

Ritu, Refer the answer key posted here: http://economicsentrance.weebly.com/lessons.html

[ritu]

so sir does that mean that even if two goods are complements we can have one's consumption to be zero?????
this forces me to think in term of car and petrol....if car price rises,and still ppl are purchasing more cars can they stop purchasing fuel?????/
(sorry for absurd example ,car being a luxury.....)

pls reply sir

[ritu]

pls reply sir...

[Amit Goyal]

Ritu, Good X is a gross complement for good Y if an increase in the price of Y causes a decrease in demand for X OR a decrease in the price of Y causes an increase in demand for X.

[ritu]

ok sir....so i was missing out on the distinction between perfect and gross complements.....
thanx a lot sir....:)))))))