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 $$R_i$$ ($$1 \leq i \leq 5$$). The average of the amounts in column j is $$C_j$$ ($$ 1\leq j \leq 4$$). What is the average of all 20 amounts on the spreadsheet?
(1) $$R_1 + R_2 + R_3 + R_4 + R_5 = 550$$
(2) $$C_1 + C_2 +.C_3 + C_4 = 440$$