几道数学题请教大家

我在做新东方的补充教材时碰到了几个问题，自己想不明白，所以想请教一下大家。多谢！

1.what is the volume of a certain rectangular solid?
(1)two adjacent faces of the solid have areas 15 and 24, respectively.
(2)each of two opposite faces of the solid has area 40.
我认为应选E，而答案却是C。我认为根据题设和条件，都不能确定是长宽高。

2.if n=p/q where p and q are nonzero integers, is n an integer?
(1)n^2 is an integer.
(2)(2n+4)/2 is an integer.
答案是D，但我觉得是 B。

3. is the integer n a multiple of 15?
(1)n is a multiple of 20.
(2)n+6 is a multiple of 3.
答案是C，我认为是E，因为比如n=60，符合条件，但却不是15的multiple.

4.the figure(直角坐标系中以原点为圆心的一个圆其中一条半径(beam)在第一象限，与x轴夹角为rº),shows the present position on a radar screen of a sweeping beam that is rotationg at a constant rate in a clockwise direction. In which of the four quadrants will the beam lie 30 seconds from now?
(1)in each 30-second period, the beam sweeps through 3.690º
(2)r=40
key:A, 但我认为是C。因为如果没有r的度数，就没有办法判断beam的present position.

5.if an organization were to sell n tickets for a theater production, the total revenue from ticket sales would be 20 percent greater than the total costs of the production. If the organization actually sold all but 5 percent of the n tickets, the total revenue from ticket sales was what percent greater than the total costs of the production?
(a) 4% (b) 10% (c) 14% (d) 15% (e) 18%
key:c why?

6. 10^3(10的三次幂) is how many times (0.01)^3
(a) 10^6 (b) 10^8 (c) 10^9 (d) 10^12 (e) 10^18
key: d, 但我认为是C.
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