请NN帮忙解一些06/11月数学JJ题目.谢谢!!!

3 - f[x] is defined to the closest number equal or less x, f[y]=2, f[x/3]=?

answer 0

(why?)

4 - ( JiHe problem - number of P is twice as M, MP together is 1/2 of M only, total number of MP together is 5000, ask P only.

Answer 10,000

(why?)

5 - DS 8^2x < 4^(y+1)?  1) x<y+1 2) 3x<2y

My asnwer is E. 

(why)

6 - Asking the total distance of a tiangle, whose 3 points are (-4, 3) (3,4) and (-1,1) on the XY-plane. It aslo said something about the points were on a lake, come with a drawing too.

Answer 17. 

(why?)

7 - DS

X is left of Y and Z, is XYZ<0?   1) XY<0 2) YX<0

E because the asnwer depends the relative position of Y and Z.

(my answer is D,am I right?)

8 - DS 700 of tickets were sold, and ticket price to the students is half that to the none-students, ask how many were sold to Students?  1)Total revinue is $2500 2) The total price of 1 student and 1 none-student ticket is $6.

C(am I right?)

9 - DS A 3-digit integer, what is the unit digit?  1)product of all units = 54 (or 56) 2)sum of all unit >16. 

No clue.

Thanks for your time!!!