3道数学题，麻烦各位帮我看看

sliton

Q25:
A photographer will arrange 6 people of 6 different heights for photograph by placing them in two rows of three so that each person in the first row is standing in front of someone in the second row.  The heights of the people within each row must increase from left to right, and each person in the second row must be taller than the person standing in front of him or her.  How many such arrangements of the 6 people are possible?

A.    5
B.    6
C.    9
D.    24
E.    36

答案 是a 为什么？

Q30:
Joanna bought only $0.15 stamps and $0.29 stamps.  How many $0.15 stamps did she buy?
(1)      She bought $4.40 worth of stamps.
(2)      She bought an equal number of $0.15 stamps and $0.29 stamps.
   
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

答案是d 为什么？


Q35:
What is the median number of employees assigned per project for the projects at Company Z?
(1)    25 percent of the projects at Company Z have 4 or more employees assigned to each project.
(2)     35 percent of the projects at Company Z have 2 or fewer employees assigned to each project.
   
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

答案是c 为什么？

感谢各位的帮助！！