Paired-position swaps – Number 53146872: swap (1↔5), (2↔6), (3↔7), (4↔8). After rearrangement, what is the 5th digit from the right end?

Introduction / Context:
Index-swapping exercises require careful mapping of original positions to new ones, then translating a right-based index to a left-based position.

Given Data / Assumptions:

• Original digits (1-based): [5,3,1,4,6,8,7,2].
• Swap pairs: (1,5), (2,6), (3,7), (4,8).

Concept / Approach:
Perform each swap pair once on the original indices. After swaps, convert “5th from right” in an 8-digit number to the left index: 8 − 5 + 1 = 4.

Step-by-Step Solution:
After swaps → [6,8,7,2,5,3,1,4].5th from right = position 4 = digit 2.

Verification / Alternative check:
Rightmost four digits are 4 (1st), 1 (2nd), 3 (3rd), 2 (4th); the next (5th from right) is indeed 2 at left index 4.

Why Other Options Are Wrong:
1/4/6/8 occur elsewhere but not at the queried position.

Common Pitfalls:
Applying swaps sequentially and reusing modified positions incorrectly; mis-converting right index to left.

Final Answer:
2