did I understand correctly, the first number is:
[tex] 4\frac{2}{7} [/tex]?
in other words, this would be:
[tex] \frac{4*7+2}{7} = \frac{30}{7} [/tex]
and if you drink half of it, then we divide this number by 2:
[tex]\frac{15}{7} [/tex]
because 30/2=15
so you would have
[tex]2 \frac{1}{7} [/tex]
still more than a daily dose!