A glass filled with water has a mass of $1000 \mathrm{~g}$. When half the water is removed from the glass, the mass of the glass and the remaining water is $700 \mathrm{~g}$. What is the mass of the empty glass?
(A) $600 \mathrm{~g}$
(B) $500 \mathrm{~g}$
(C) $350 \mathrm{~g}$
(D) $400 \mathrm{~g}$
(E) $300 \mathrm{~g}$
When half of the water is removed from the glass, the mass decreases by $1000-700=300 \mathrm{~g}$. In other words, the mass of half of the original water is $300 \mathrm{~g}$.

Therefore, the mass of the empty glass equals the mass of the half-full glass, minus the mass of half of the original water, or $700-300=400 \mathrm{~g}$.

ANSWER: (D)