Lesson: Data Sufficiency Challenging - 16t07

Easy Math/Tough Applications: Example 1

Challenging questions in the Quantitative Section may test your ability to cut through dense information to get to the heart of what often turns out to be a relatively simple matter. Why does the Exam do this? To see whether you have the ability to whittle complex language down to an easy solution. In these problems, the important thing is to find the "question behind the question." That is, to find what the question is really asking. Here’s an example:

At the end of every hour a culture of bacteria becomes some number of times larger than it was the previous hour. If the number of bacteria was originally greater than 1 and if the rate of growth also increases every hour, what was the original number of bacteria?

1) of the original culture would have resulted in a total of 385 bacteria after 3 hours.

2) The original number of bacteria was less than 4.

Review the question stem above. Do you recognize the math concept that this is testing? Type it into the Text Box, and click Continue.

This problem is really about .

Review Statement 1 below. Is it sufficient or insufficient? Select the correct answer and then click Continue.

1) of the original culture would have resulted in a total of 385 bacteria after 3 hours.?

Sufficient

Insufficient

Review Statement 2 below. Is it sufficient or insufficient? Select the correct answer and then click Continue.

2) The original number of bacteria was less than 4.

Sufficient

Insufficient

Review the statements in combination. Are they sufficient or insufficient? Select the correct answer and then click Continue.

1) of the original culture would have resulted in a total of 385 bacteria after 3 hours.

2) The original number of bacteria was less than 4.

Sufficient

Insufficient

Countinue

Putting the statements together allows us to figure out that the original number of bacteria must have been 3. Statement 1 says that the original number of bacteria had to be either 3, 5, 7 or 11. Statement 2 says that the original number of bacteria was less than 4, while the stem says that it was greater than 1, so only 3 satisfies all criteria. Which means that in combination the statements are sufficient.

You can see that this wasn’t a very difficult problem mathematically. The real difficulty was knowing how to approach the question. Thinking a little bit about what mathematical concepts lurk behind a question is usually the best way to get the ball rolling.

Let’s try another.

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