Răspuns :
1. S = 1 + 3 + 5 +.........+ 19
S1 = 2+ 4 + 6 +.............+18 = 2(1 + 2 + 3+.......+9) = 2·9·10/2 = 90
S + S1 = 1 + 2 + 3 +.4+.....+19 = 19·20/2 = 190
S + 90 = 190 S = 100
2. 8/3 + x = 22/3
8 + 3x = 22 3x = 14 x = 14/3
S1 = 2+ 4 + 6 +.............+18 = 2(1 + 2 + 3+.......+9) = 2·9·10/2 = 90
S + S1 = 1 + 2 + 3 +.4+.....+19 = 19·20/2 = 190
S + 90 = 190 S = 100
2. 8/3 + x = 22/3
8 + 3x = 22 3x = 14 x = 14/3