No, it's not a number of pounds, it's a fraction of a box.
Katherine has eaten
of a box of candy.
Therefore what's left after that is
1 box -
of a box =
of a box -
of a box =
of a box.
she gives Mary 1/2 of the remainder
So half of
is
or
of a box.
That's how much she gives Mary and that's also how much she has left.
Edwin