请教几道GWD数学题

pausa1087

1. A certain characteristic in a large population has a distribution that is symmetric about the mean m.  If 68 percent of the distribution lies within one standard deviation d of the mean, what percent of the distribution is less than m +d ?

A.     16%

B.     32%C.     48%

D.     84%

E.      92%

答案是D。但是题目意思没有读懂，烦请赐教。

2. How many 4-digit positive integers are there in which all 4 digits are even?A.     625

A.     625

B.     600

C.     500

D.     400

E.      256

答案是C。请教此题的演算过程。

3. A school administrator will assign each student in a group of n students to one of m classrooms.  If 3 < m< 13 < n, is it possible to assign each of the n students to one of the m classrooms so that each classroom has the same number of students assigned to it?(1)   It is possible to assign each of 3n students to one of m classrooms so that each classroom has the same number of students assigned to it.

(2)   It is possible to assign each of 13n students to one of m classrooms so that each classroom has the same number of students assigned to it.

答案是B。但是题目没有看懂。

烦请NN请教，谢谢！