Q4:

A total of 20 amounts are entered on a spreadsheet that has 5 rows and 4 columns; each of the 20 positions in the spreadsheet contains one amount.  The average (arithmetic mean) of the amounts in row i is R_i (1 ≤ i ≤ 5).  The average of the amounts in column j is C_j (1 ≤ j ≤ 4).  What is the average of all 20 amounts on the spreadsheet?

(1)     R₁ + R₂ + R₃ + R₄ + R₅ = 550

(2)     C₁ + C₂ + C₃ + C₄ = 440

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.

题目不理解，那位好心人给俺讲讲啊，万分感谢

20个数据填入一个5行x4列的表格，每格填一个。第i行的数学平均值为Ri(1<=i<=5)，第j列的数学平均值为Cj(1<=j<=4)，问整个表格里20个数据的平均值是多少。

选D吧？