A7. If we fill the pot with water to the top, it weighs $17 \mathrm{~kg}$, but if we fill it with water to half, it weighs $9.5 \mathrm{~kg}$. How much does the empty pot weigh?
(A) $0.5 \mathrm{~kg}$
(B) $1 \mathrm{~kg}$
(C) $1.5 \mathrm{~kg}$
(D) $2 \mathrm{~kg}$
(E) $3 \mathrm{~kg}$
A7. From the text of the problem, we can write a system of two equations: $p+v=17$ and $p+\frac{1}{2} v=9.5$. The pot $p$ weighs $2 \mathrm{~kg}$, and the water in it weighs $15 \mathrm{~kg}$.