Is x > y? a) x – y = 10 b) y = 5

Concept: In a Data Sufficiency question, a statement is sufficient on its own only when it forces exactly one answer — always "yes" or always "no" — for every value consistent with it, independent of the other statement. A statement that leaves the comparison genuinely open, or leaves a variable completely unconstrained, is not sufficient by itself; each statement must be tested on its own before checking whether both are needed together.

Application: Test each statement independently against the question "Is x > y?"

1. Statement A: x − y = 10 rewrites as x = y + 10. Since 10 is positive, x is always exactly 10 more than y, whatever value y takes. This forces the answer to "yes" every time — Statement A alone is sufficient.

2. Statement B: y = 5 fixes only y. It places no restriction on x at all, so x could be less than, equal to, or greater than 5. The comparison stays open — Statement B alone is not sufficient.

Cross-check: Statement A alone already forces a definite "yes", so the correct classification is Statement A alone is sufficient — not "either" (which would need Statement B to also stand alone) and not "both are required" (which would need Statement A to fail alone, which it does not).