Niu Niu drinks milk as much as water, both of which are one cup.

1, Niu Niu started to drink 1 whole glass of milk, and later only added water without milk, so Niu Niu drank 1 times the milk.

It can be verified by the amount of milk Niu Niu drinks three times as follows:

1/2+( 1/2x 1/2)+( 1/2x 1/2)= 1/2+ 1/4+ 1/4 = 1

2. Water is added twice in the whole process, each time 1/2 cups and twice 1 cup (1/2+ 1/2= 1).

It can also be calculated by the amount of water she drinks twice:

( 1/2x 1/2)+( 1/2+ 1/2x 1/2)

= 1/4+ 1/2+ 1/4

= 1