What is the monthly salary of Praveen? Consider the following statements: I. Praveen receives 15 percent more salary than Sumit, while Sumit receives 10 percent less than Lokesh. II. Lokesh has a monthly salary of Rs 2500.

Introduction / Context:
This data sufficiency question involves salaries of three people: Praveen, Sumit, and Lokesh. Their salaries are related by given percentages, and the final goal is to find Praveen monthly salary. The two statements provide relative and absolute information. We need to judge whether each statement alone or their combination is enough to compute Praveen salary uniquely.

Given Data / Assumptions:

• Statement I: Praveen receives 15 percent more salary than Sumit, and Sumit receives 10 percent less than Lokesh.
• Statement II: Lokesh monthly salary is Rs 2500.
• Salaries are positive amounts measured in rupees.
• Monthly salary refers to a fixed amount with no hidden components beyond what is described.

Concept / Approach:
Let L denote Lokesh salary, S denote Sumit salary, and P denote Praveen salary. Statement I expresses S and P as percentages of L and S respectively. Statement II gives the numerical value of L. Once L is known, S follows from the percent relation, and P follows from S. The question is whether any statement alone can provide the required numeric base or whether both are needed.

Step-by-Step Solution:
Step 1: Translate statement I into equations. If Sumit receives 10 percent less than Lokesh, then S = L * (1 minus 0.10) = 0.90 * L. If Praveen receives 15 percent more than Sumit, then P = S * (1 plus 0.15) = 1.15 * S. Step 2: Substitute S into P. We get P = 1.15 * (0.90 * L) = 1.035 * L. So Praveen salary is 1.035 times Lokesh salary. Step 3: Statement I alone gives only proportional relationships with L as a free variable. Without a numeric value for L, P cannot be computed exactly. Therefore statement I alone is not sufficient. Step 4: Consider statement II alone. It states that L = Rs 2500. However, without the percentage relationships from statement I, we do not know how P compares to L, so we still cannot compute P. Statement II alone is also not sufficient. Step 5: Combine statements I and II. From II, L = 2500. Using the formula P = 1.035 * L derived from I, we get P = 1.035 * 2500. Step 6: Multiply to find P. 1.035 * 2500 equals 2587.50 rupees. Thus Praveen monthly salary is Rs 2587.50, and this value is uniquely determined when both statements are used together.

Verification / Alternative check:
From a sufficiency perspective, note that three salaries are linked by two percentage relations in statement I. This single statement reduces the degrees of freedom but still leaves L undetermined. Statement II provides the missing numeric value for L. With both pieces, there is no remaining free variable. In contrast, each statement alone leaves also at least one variable free and therefore cannot yield a unique value for P, which confirms that both are required.

Why Other Options Are Wrong:
Option A is incorrect because statement I alone provides only relationships, not numbers. Option B is incorrect since statement II alone provides a number but no relationship to Praveen. Option C incorrectly claims that either statement alone is sufficient. Option E, which says that even both statements together are not sufficient, clearly conflicts with the exact computation of P. Only option D correctly indicates that both statements I and II together are necessary and sufficient.

Common Pitfalls:
Learners may misinterpret phrases like 10 percent less and 15 percent more, for example by subtracting or adding the same amount independently of the base. Another typical error is to assume that knowing Lokesh salary immediately gives Praveen salary without applying the intermediate relation through Sumit. Carefully writing out percentage equations avoids these mistakes.

Final Answer:
The data in both statements I and II together are necessary to answer the question, so the correct option is D.