Question

向一个已装满三分之一的水箱中加入四加仑水后，水箱变为装满一半。这个水箱的容量是多少加仑？

When four gallons are added to a tank that is one-third full, the tank is then one-half full. The capacity of the tank in gallons is

$8$

$12$

$20$

$24$

$48$

加入的 $4$ 加仑对应从 $\dfrac13$ 满到 $\dfrac12$ 满的增加量，即容量的 $\dfrac12 - \dfrac13 = \dfrac16$ 。

如果容量的 $\dfrac16$ 是 $4$ 加仑，那么总容量是 $4 \times 6 = 24$ 加仑。

所以正确答案是 D。

The $4$ gallons account for the change from $\dfrac13$ full to $\dfrac12$ full, which is $\dfrac12 - \dfrac13 = \dfrac16$ of the capacity.

If $\dfrac16$ of the capacity is $4$ gallons, the full capacity is $4 \times 6 = 24$ gallons.

Thus, the correct answer is D .