Single-student two-sided rank – Neha is 21st from the top and 30th from the bottom in her class. What is the total number of students?

Introduction / Context:
When both top-rank and bottom-rank of the same student are given, the class size is the sum minus one: N = top + bottom − 1.

Given Data / Assumptions:

• Neha’s ranks: 21st from top, 30th from bottom.

Concept / Approach:
For a single lineup, positions counted from both ends overlap on the student herself once; hence subtract one to avoid double counting.

Step-by-Step Solution:
N = 21 + 30 − 1 = 50.

Verification / Alternative check:
Check: If there are 50 students, the 21st from top is the 30th from bottom (since 50 − 21 + 1 = 30). Consistent.

Why Other Options Are Wrong:
48/49/51 would break the complement relation between the two given ranks.

Common Pitfalls:
Forgetting to subtract one.

Final Answer:
50