Data Sufficiency

I just took the first GMAC Official Practice Test and am trying to figure out the ones I got wrong.

Warehouse W's revenue from the sale of sofas was what percent greater this year than it was last year?

(1) Warehouse W sold 10 percent more sofas this year than it did last year.

(2) Warehouse W's selling price per sofa was $30 greater this year than it was last year.

The answer is E, why isn't it C?

Thanks!

## GMAT Prep Practice Test Quant Questions #2

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### GMAT/MBA Expert

- ceilidh.erickson
- GMAT Instructor
**Posts:**2094**Joined:**04 Dec 2012**Thanked**: 1443 times**Followed by:**247 members

We can TEST CASES to prove insufficiency in this problem.

Revenue from sales will equal (price of sofas)(quantity sold) --> R = (p)(q)

To answer the question of the proportional difference in revenue, we need to know:

- what was the proportional difference in price?

- what what the proportional difference in quantity sold?

This doesn't tell us anything about price. If we sold 10% more sofas at the same price, we'd make 10% more revenue. But if price also went up 10%, then:

(1.1p)(1.1q) = 1.21pq --> 21% increase in revenue

Insufficient.

This doesn't give us any information about how many were sold. We might have sold half as many as last year... or twice as many. Those would give us very different answers about the change in revenue.

Insufficient.

We know the proportional increase in quantity sold, and a numerical difference in price. Let's compare 2 different scenarios:

Scenario A (cheap couches):

last year: sold 100 couches at $100 each --> $10,000 in revenue

this year: sold 110 couches at $130 each --> $14,300 in revenue

43% increase in revenue

Scenario B (very expensive couches):

last year: sold 10,000 couches at $10,000 each --> $100,000,000 in revenue

this year: sold 11,000 couches at $10,030 each --> $110,330,000 in revenue

Barely more than a 10% increase in revenue

Because we don't know what that +$30 means as a PROPORTIONAL difference, we don't know the proportional change to the revenue.

The answer is E.

*Warehouse W's revenue from the sale of sofas was what percent greater this year than it was last year?*Revenue from sales will equal (price of sofas)(quantity sold) --> R = (p)(q)

To answer the question of the proportional difference in revenue, we need to know:

- what was the proportional difference in price?

- what what the proportional difference in quantity sold?

**(1) Warehouse W sold 10 percent more sofas this year than it did last year.**This doesn't tell us anything about price. If we sold 10% more sofas at the same price, we'd make 10% more revenue. But if price also went up 10%, then:

(1.1p)(1.1q) = 1.21pq --> 21% increase in revenue

Insufficient.

**(2) Warehouse W's selling price per sofa was $30 greater this year than it was last year.**This doesn't give us any information about how many were sold. We might have sold half as many as last year... or twice as many. Those would give us very different answers about the change in revenue.

Insufficient.

**(1) and (2) together**We know the proportional increase in quantity sold, and a numerical difference in price. Let's compare 2 different scenarios:

Scenario A (cheap couches):

last year: sold 100 couches at $100 each --> $10,000 in revenue

this year: sold 110 couches at $130 each --> $14,300 in revenue

43% increase in revenue

Scenario B (very expensive couches):

last year: sold 10,000 couches at $10,000 each --> $100,000,000 in revenue

this year: sold 11,000 couches at $10,030 each --> $110,330,000 in revenue

Barely more than a 10% increase in revenue

Because we don't know what that +$30 means as a PROPORTIONAL difference, we don't know the proportional change to the revenue.

The answer is E.

Ceilidh Erickson

EdM in Mind, Brain, and Education

Harvard Graduate School of Education

EdM in Mind, Brain, and Education

Harvard Graduate School of Education

### GMAT/MBA Expert

- ceilidh.erickson
- GMAT Instructor
**Posts:**2094**Joined:**04 Dec 2012**Thanked**: 1443 times**Followed by:**247 members

In DS, the GMAT often likes to mix up PROPORTIONS v. REAL NUMBERS. Generally speaking, a real number won't help to answer a proportion question (unless you're give more info).

Here are more in a similar vein to try:

https://www.beatthegmat.com/by-what-per ... tml#790569

https://www.beatthegmat.com/ds-5-t275286.html#717201

https://www.beatthegmat.com/if-the-salt ... tml#807915

https://www.beatthegmat.com/in-the-figu ... tml#825835

https://www.beatthegmat.com/how-to-choo ... tml#695925

Here are more in a similar vein to try:

https://www.beatthegmat.com/by-what-per ... tml#790569

https://www.beatthegmat.com/ds-5-t275286.html#717201

https://www.beatthegmat.com/if-the-salt ... tml#807915

https://www.beatthegmat.com/in-the-figu ... tml#825835

https://www.beatthegmat.com/how-to-choo ... tml#695925

Ceilidh Erickson

EdM in Mind, Brain, and Education

Harvard Graduate School of Education

EdM in Mind, Brain, and Education

Harvard Graduate School of Education