What was a certain company's revenue last year?

[BTGModeratorVI]

What was a certain company's revenue last year?

(1) Last year gross profit was $4,100
(2) Last year revenue was 50% greater than expenses

Answer: C
Source: GMATPrep

[Brent@GMATPrepNow]

What was a certain company's revenue last year?

(1) Last year gross profit was $4,100
(2) Last year revenue was 50% greater than expenses

Answer: C
Source: GMATPrep

Target question: What was a certain company's revenue last year?
Key concept: revenue - expenses = profit

Statement 1: Last year gross profit was $4,100
Since we have no information about the expenses, there is no way we can answer the target question.
Statement 1 is NOT SUFFICIENT

If you're not convinced consider these two possible cases that satisfy statement 1:
Case a: expenses = $1000 and profit = $4100. Since revenue - expenses = profit, we can write: revenue - $1000 = $4100, which means revenue = $5100
Case b: expenses = $2000 and profit = $4100. Since revenue - expenses = profit, we can write: revenue - $2000 = $4100, which means revenue = $6100
Since we cannot answer the target question with certainty, statement 1 is NOT SUFFICIENT

Statement 2: Last year revenue was 50% greater than expenses
There are many scenarios that satisfy statement 2. Here are two:
Case a: expenses = $100 and revenue = $150 (notice that revenue is 50% greater than expenses). In this case, the answer to the target question is revenue = $150
Case b: expenses = $10 and revenue = $15 (notice that revenue is 50% greater than expenses). In this case, the answer to the target question is revenue = $15
Since we cannot answer the target question with certainty, statement 2 is NOT SUFFICIENT

Statements 1 and 2 combined
Statement 2 tells us that revenue was 50% greater than expenses. So, if we let x = expenses, then 1.5x = revenue
Statement 1 tells us that profit = $4,100
Since revenue - expenses = profit, we can write: 1.5x - x = $4100
At this point, we COULD solve this equation for x, which means we COULD answer the target question with certainty (of course, on test day, he would never waste our time solving the equation, since we need only determine whether or not we have sufficient information to answer to Target question)

For "fun" let's solve the equation 1.5x - x = $4100
Simplify the left side to get: 0.5x = $4100
Divide both sides by 0.5 to get: x = $8200
Since 1.5x = revenue, we know that the revenue = 1.5($8200) = $12,300
Since we can answer the target question with certainty, the combined statements are SUFFICIENT

Answer: C

Cheers,
Brent