Say, I have a packet of milk and there is not much left in it. If I pour it in a cup, it might less than 1/4 filled.
Can I describe it like this
There is less than one fourth of a cup of milk in the packet.
Or in another context
The amount of juice in the box will be slightly more than three fourth of a cup.
Also, should I use a or the with cup? one fourth of a cup or one fourth of the cup?