How many students are there between Suresh and Mohan in a row of 50 students? I. Suresh is twelfth (12th) from the left end and Mohan is seventeenth (17th) from the right end. II. Suresh is six places away from Jayesh, who is twentieth (20th) from the left end.

Introduction / Context:
This Data Sufficiency problem asks for the exact number of students between two named positions in a fixed-length row (50 students). We must judge whether each statement provides enough information independently, or only together, or neither.

Given Data / Assumptions:

• Total students in the row = 50.
• I: Suresh is 12th from the left end; Mohan is 17th from the right end.
• II: Suresh is 6 places away from Jayesh; Jayesh is 20th from the left.

Concept / Approach:
For position conversions, use: position_from_left = N - position_from_right + 1, where N = 50. The count of people strictly between two positions L1 and L2 (from the same end) is abs(L1 - L2) - 1. Data Sufficiency focuses on the adequacy of information rather than repetitive arithmetic.

Step-by-Step Solution:

Verification / Alternative check:
Recompute between-count carefully to avoid off-by-one mistakes; “between” excludes end positions themselves.

Why Other Options Are Wrong:

• B: II lacks Mohan’s position and thus cannot determine the gap.
• C: Not “either alone”; only I suffices.
• D/E: Not required since I alone is already sufficient.

Common Pitfalls:
Mixing “between” with inclusive counts; forgetting to convert right-to-left positions correctly; mishandling the ±6 ambiguity in II.

Final Answer:
Statement I alone is sufficient; Statement II alone is not.