the overall atomic mass is 204.37, but for thallium 203 it is 203, and for thallium 205, it is 205.
The number 203 and 205 have no common factors. 203 = 7 x 29 205 = 5 x 41
101.5
205
34.1667
Find the average of your readings. Divide 220 volts into it and you will have your answer.
67.6667
1.1429
203
3 x 203 = 609.
0.0197
25.375