**Concept:** **The question is a word problem expressed as a DS question**

**Solution**

To answer this, we require (a) either the number of books sold at full price or half price and (b) the value of full price or the half price.

If a is the books sold at full price b, then the revenue will be a*b + (2000 - a) * b/2**Statement 1::** Four times as many books were sold at full price as were sold at half price.

From this we can find the number of books sold at full and half the price.

If x = number of books sold at half price, then 4x is the number of books sold at full price.

Then 4x + x = 2000 and x = 400

Answer options could be B, C or E. Therefore Statement 1 Alone is **Insufficient.**

**Statement 2:** The full price of a book was $10.

From this we cannot get the number of books sold at half or full price

Answer Options could be C or E. Therefore Statement 2 Alone is **Insufficient.**

**Combining Both Statements: **

Number of books sold at full price $10 is 1600 and number of books sold at half price $5 is 400, with which we can find the revenue.

Therefore Both Statements together are **Sufficient.****Option C**