gwd 21-8 ,21,25 no explanations in gwd link

Q8:

The number of defects in the first five cars to come through a new production line are 9, 7, 10, 4, and 6, respectively.  If the sixth car through the production line has either 3, 7, or 12 defects, for which of theses values does the mean number of defects per car for the first six cars equal the median?

I.                    3

II.                 7

III.               12

A.   I only

B.    II only

C.   III only

D.   I and III only

E.    I, II, and III

why is d,it's aweful that i chose b!

A store purchased a Brand C computer for the same amount that it paid for a Brand D computer and then sold them both at higher prices.  The store’s gross profit on the Brand C computer was what percent greater than its gross profit on the Brand D computer?

(1)   The price at which the store sold the Brand C computer was 15 percent greater than the price at which the store sold the Brand D computer.

(2)     The store’s gross profit on the Brand D computer was $300.

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.

why is e?

If M is the least common multiple of 90, 196, and 300, which of the following is NOT a factor of M ?

A.        600

B.        700

C.        900

D.     2,100

E.      4,900

in my opinion ,there's no correct answer~why is a?

thank you so much!!