Explanation
The series can be analyzed by dividing the sequence of symbols into figures (groups) of three symbols each:
Figure 1: 5, A, X
Figure 2: 5, ☐, A
Figure 3: R, R, 5
Figure 4: A, ☐, R
Figure 5: R, A, 5
Figure 6: X, X, ☐
An analysis of these figures reveals a clear pattern:
Every third figure (3, 6, 9...) consists of a doubled symbol and one other symbol, excluding A. Figure 3 has a doubled R (R, R, 5) and Figure 6 has a doubled X (X, X, ☐).
The remaining figures (1, 2, 4, 5, 7...) always contain the symbol A and two other symbols from the set {5, X, ☐, R}.
The position of A within these figures follows a repeating cyclic shift:
In Figure 1, A is in the 2nd position.
In Figure 2, A is in the 3rd position.
(Figure 3 is skipped).
In Figure 4, A is in the 1st position.
In Figure 5, A is in the 2nd position.
(Figure 6 is skipped).
Following this pattern, in Figure 7, A must be in the 3rd position.
The other two symbols in these figures follow a specific sequence:
The first symbol of the pairs follows a doubled pattern: (5, 5), (R, R), (X, X), (☐, ☐). For Figures 1 and 2, it is 5; for Figures 4 and 5, it is R; for Figure 7, the next in sequence is X.
The second symbol follows a similar pattern starting from X: X, (☐, ☐), (5, 5), (R, R). For Figure 1, it is X; for Figures 2 and 4, it is ☐; for Figures 5 and 7, the next in sequence is 5.
Combining these, Figure 7 consists of X in the 1st position, 5 in the 2nd position, and A in the 3rd position, resulting in X5A.