明天就考了，prep数学竟然错了好几道……求助几道数学

if n is a multiple of 5 and n=p^2q, where p and q are prime numbers, which of the following must be a multiple

of 25   

A p^2  B q^2  C pq  D p^2q^2  E P^3q^3



a company plans to assign identification numbers to its employees. each number is to consist of four different

digits from 0 to 9, inclusive, except that the first digit cannot be 0. How many different identification

numbers are possible?
A 3024  B 4536   C 5040  D  9000  E 10000



the
positive integer k has exactly two positive prme factors, 3 and 7 if k
has a total of 6 positive factors, including 1 and k, what is the value
of k?
1. 3^2 is a factor of k
2.  7^2 is not a factor of k



are at least 10 percent of the people in country X who are 65 years old or older employed?
1.   in country x  11.3 percent of the population is 65 years old or older.
2.   in country x   of the population 65 years old or older, 20 percent of the men and 10 percent of the women are employed.



of the 1400 college teachers surveyed, 42 percent said they considered engaging in research an essential goal.

How many of the college teachers surveyed were women?
1. 
in the survey, 36 percent of the men and 50 percent of the women said
that they considered engaging in research an essential goal.
2.  in the survey, 288 men said that they considered engaging in research an essential goal.