Q30:

A certain database charges users a registration fee of x dollars, and if charges registered users y dollars per file downloaded.  If there are no other charges for users of this database, what is the amount of the registration fee?

(1)     The total charge to download 50 files is $150, including the registration fee.

(2)     The total charge to download 100 files is $225, including the registration fee.

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.

为什么是C,不是还有个前提条件 if charges registered users y dollars per file downloaded.

(1)x+50y=150

(2)x+100y=225

二元一次方程要联系才能