Hi to all!!! I have problems in understanding the answers to also these questions (which i put in bold)

Could you please help me out in explaining them to me??

I managed to finish these sets, these are the last questions about them..

thanks alot!!

Riccardo

Q8:

An equilateral triangle that has an area of 9√3 is inscribed in a circle. What is the area

of the circle?

A. 6pi

B. 9pi

C. 12pi

D. 9pi √3

E. 18pi √3

Q16:

In the sequence of nonzero numbers t1, t2, t3, â€¦, tn, â€¦, tn+1 = tn / 2 for all positive integers

n. What is the value of t5?

(1) t3 = 1/4

(2) t1 - t5 = 15/16

Answer is C, but canâ€™t u find it out also with each alone? (I chose D)

Q16:

If n is an integer greater than 6, which of the following must be divisible by 3?

A. n*(n+1)*(n-4)

B. n*(n+2)*(n-1)

C. n*(n+3)*(n-5)

D. n*(n+4)*(n-2)

E. n*(n+5)*(n-6)

SET 29

Q9:

A total of 100 customers purchased books at a certain bookstore last week. If these

customers purchased a total of 200 books, how many of the customers purchased only 1

book each?

(1) None of the customers purchased more than 3 books.

(2) 20 of the customers purchased only 2 books each.

Answer is C.. but actually shouldnâ€™t it be E?

Q16:

On a certain nonstop trip, Marta averaged x miles per hour for 2 hours and y miles per

hour for the remaining 3 hours. What was her average speed, in miles per hour, for the

entire trip?

(1) 2x + 3y = 280

(2) y = x + 10

Answer is Aâ€¦

SET 31

Q18:

2x + y = 12

|y| less or equal than 12

6

For how many ordered pairs (x , y) that are solutions of the system above are x

and y both

integers?

A. 7

B. 10

C. 12

D. 13 E. 14

Q26:

What is the greatest common factor of the positive integers j and k?

(1) k = j + 1

(2) jk is divisible by 5.

Answer is D, why??