Each piglet in a litter is fed exactly one-half pound of a

I'm not sure if this is a trick, but just reading the question and statements tells us from Piglet A, there is no way we can tell how many piglets there are.

Click E and carry on to the next question.

definitely there are 4 piglets but could be more than 4.

OA=C There must have been 5 piglets

I agree with 'C'.

Statement1: This gives information about the Oats only. We are not sure how much was the Barley's proportion. So INSUFF

Statement2: Same as above. It doesn't give info about the oats' proportion.

Taking them together:

let total number of piglets are p
Total quantity of oat = x
Total quantity of barley= y
Putting the both statements in equation,
for one piglet
x/4+ y/6 = 1/2 it can be written as
9x + 6y = 18 ------------------(1)

remaining piglets = p -1
p-1 piglets are left with 3x/4 of oats and 5y/6 of barley.
putting in eq. 3x/4 + 5y/6 = (1/2)(p-1)
solving it, 9x +10y = 6p -6 ---------(2)

Solving eq 1 and 2
p = (2y/3) + 4

It means the piglets will be more than 4.
as p is a +ve integer, 2y/3 will be +ve integer. possible values of y = 1.5,3,4.5,6....
from equation1 6y < 18
hence y < 3
so y is 1.5.

That means total number of piglets = 1 + 4 = 5

This is fabulous! Another way to is realise that A must get greater than the average quantity of oats and less than the average quantity of barley or vice versa