@ srk, ans is 2.
@ Anant sir, - I think it can also be got from what I did. If the last part of my soln is unclear, then I'm elaborating it here.
As already said, in the union of A,B,C there must be 2 elements that are not present in any of the sets, let me set set A as my reference.
Let these "new" elemenets be x and y.
Also let m of these elements be in B and n in C.
CASE -1, m>n.
(m,n)=(2,1).
So that gives \left|A\cup C \right|=100.
\left|A\cup B \right|=98 & \left|C\cup B \right|=99.
Also \boxed{ \sum{\left|C\cup B \right|}=297}....(1).
CASE-II m=n.
a) x in B, y in C.
b) x,y present in both sets B and C, that in the previous fashion gives a) \sum{|A\cap B|}>297 & for b) \sum{|A\cap B|}=297.
CASE 3 when n>m. (n,m)=(2,0) (2,1) - in similar fashion we have for (n,m)=(2,0) \sum{|A\cap B|}> 297 & for (n,m)=(2,1) \sum{|A\cap B|}= 297.
Thus minimum {|A\cap B \cap C|}= 297-\left(\sum{|A|} \right)+\sum{|A\cup B\cup C|} =98.
Now pls reply, whether correct or not.