Official Guide Explanation:
Data Sufficiency #117




This is just one of hundreds of free explanations I've created to the quantitative questions in The Official Guide for GMAT Quantitative Review (2nd ed.). Click the links on the question number, difficulty level, and categories to find explanations for other problems.

These are the same explanations that are featured in my "Guides to the Official Guide" PDF booklets. However, because of the limitations of HTML and cross-browser compatibility, some mathematical concepts, such as fractions and roots, do not display as clearly online.

Click here for an example of the PDF booklets. Click here to purchase a PDF copy.


Solution and Metadata

Question: 117
Page: 161
Difficulty: 5 (Moderate)
Category 1: Word Problems > Other >
Category 2: Word Problems > Rate Problems > Speed

Explanation: Statement (1) is insufficient. The rate of leakage might come in handy later, but it gives us no clue as to how much water was in the tank.

Statement (2) is also insufficient. The time it took to empty might also be handy in conjunction with other information, but on its own, it doesn't help us determine how much water was in the tank.

Taken together, the statements are still sufficient. It's a classic rate question. We're looking for the amount, and the statements give us time and rate. However, note that the time is given as an inequality, so we won't get a solid answer, just a range of possible answers.

Start by converting 30 gallons to ounces: as the question tells us, it's (30)(128) ounces. (Don't do the math until you have to!) Next, convert the rate to hours instead of minutes: (6.4)(60). Using the rate formula:

amount = rate * time

amount = (6.4)(60)(12) [we're using 12, but remember (2) tells us "less than 12," so this expression will give us the maximum amount.]

amount = 4608

Because of the inequality in (2), we know that the amount is less than 4,608 ounces. The question asks us whether the water in the tank is more than 30(128) = 3840 ounces. It's possible, but it might not be. Choice (E) is correct.

Click here for the full list of GMAT Quant Review explanations.


You should follow me on Twitter. While you're at it, take a moment to subscribe to GMAT Hacks via RSS or Email.

Total GMAT Math

The comprehensive guide to the GMAT Quant section. It's "far and away the best study material available," including over 300 realistic practice questions and more than 500 exercises!
Click to read more.