新手问数学。。。。表笑我

我刚开始准备GMAT,很久不碰数学了，上来就晕了。望达人指教。

答案是两个陈述都对，第一个陈述我可以得出，就是不知道2）是怎么算的。

The storage capacity of computer disk A is 85percent  that of disk B ,What percentage of disk B storage capacity is currently in use?

1) Disk B holds 3 more gigabytes than disk A

2) 8.5 gigabytes of disk B's storage capacity currently in use.

我觉得应该是C 吧

1）Suppose the capacity
of disk A is A, and the capacity of disk B is B, we can get the following equations.

      A = 85%B

      B= A +3

Solve the equations, A=17, B=20. However, we don’t know how much
of disk B’s storage capacity currently in use. It is not sufficient.

2) We only know the capacity of disk B that is currently in use.
However, no information about B’s total capacity. This is not sufficient.

1) & 2) together, we can get the percentage: 8.5/20 = 42.5%