Question

A cup is $\frac{1}{3}$ full of milk. What part of the cup is still to the filled milk to make it full?

Answer 1

let the total fill required of cup of milk is $1$
$\therefore$ Cup is $\frac{1}{3}$ full of milk.
Still to be filled by milk $\Rightarrow 1-\frac{1}{3}=\frac{3-1}{3}=\frac{2}{3}$