Lesson: Rephrasing the Target Question

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Question at 5:23 - this is a Yes or No question. In other videos, it was stated that the value is unimportant. The question ask "Does statement 2 provides us with enough information?" and it does. X is NOT less than 0. Should be SUFFICIENT 
gmat-admin's picture

In order to conclude that statement 2 is sufficient, it must be the case that we can answer the rephrased target question (Is x < 0?) with absolute certainty.

Statement 2 essentially tells us that x < 2.5. This information does not allow us to answer the rephrased target question (Is x < 0?) with absolute certainty.

Consider these two cases:
case a: x = -1, in which case x IS less than 0
case b: x = 1, in which case x is NOT less than 0.
Since we can't answer the rephrased target question with certainty, statement 2 is not sufficient.

I was thinking the same thing. I'm so confused now.
gmat-admin's picture

Can you tell what part of the explanation is confusing you?

could you please explain me in Tahir's question 03:45
How P-B = 10,000. i.e please make me understand how statement 2 is sufficient.
gmat-admin's picture

P = total pay and B = base salary
Statement 2 says the total pay (P) is 10,000 greater than the base salary (B)
So, we can write: P = B + 10,00
Another way to say this is P-B = 10,000
We phrased the question earlier to be, "What is the value of (P-B)/0.05
Since we now know that P-B = 10,000, we'll take (P-B)/0.05 and replace P-B with 10,000 to get: 10,000/0.05
This evaluates to be 200,000, which means we have successfully answered the rephrased target question. SUFFICIENT

@7:25... I'm having trouble understanding the reasoning to deduce that the question is asking if k is a non prime number.
gmat-admin's picture

We might ask ourselves, "What are some numbers that CAN be expressed as the product of two integers, where each integer is greater than 1?"

6 works, since we can write 6 = 2 x 3 (2 and 3 are both greater than 1)
20 works, since we can write 20 = 4 x 5 (4 and 5 are both greater than 1)
36 works, since we can write 36 = 6 x 6
70 works, since we can write 70 = 7 x 10

Now ask, "What are some numbers that CANNOT be expressed as the product of two integers, where each integer is greater than 1?"
Well, 5 is one such number. We CANNOT write 5 as the product of two integers, where each integer is greater than 1.
11 is another such number.
So is 2, and so is 5.

Notice that the numbers that CAN expressed as the product of two integers (where each integer is greater than 1) are all COMPOSITE numbers, and the numbers that CANNOT expressed as the product of two integers (where each integer is greater than 1) are all PRIME numbers.

Hello, could you explain me which formula is involved in the exercise @10:48 (circle), please?
gmat-admin's picture

That formula/rule is in our Circle Properties video (https://www.gmatprepnow.com/module/gmat-geometry/video/880) starting around 2:30

Euro's picture

Great material, I have suggestion or two. First can you please change the colors on the "flag this video" option. I am color, to some degree, and the red and I assume dark green flags are very close in color. Second, in this video you mentioned reviewing other material to check my knowledge. I am going in order listed so I have not reviewed the circle material yet. Thanks.
gmat-admin's picture

Sorry to hear that the red (activated) flags appear the same as the flags that aren't activated. One way to get around this is to manually note the videos you'd like to revisit (e.g., Statistics video #7).

As for your second question, it's important to note that this video appears very early in the course. So, many of the questions we're looking at in this video involve concepts that are covered later in the course. So, in the video, I encourage students to return to this video once they cover certain concepts (e.g., circle properties) in the future.

@GMAT-Admin :I would like to know where I can find seperate categorised Data Sufficiency Questions to practice so as to apply the content of the above Data Sufficiency Videos.
gmat-admin's picture

Hi Sophia,

I have used the technique of rephrasing the target question TONS of times on the Beat The GMAT forum and on the GMAT Club forum.

So, if you go to those forums and search "rephrasing the target question," you'll find over 100 questions where I've used that technique.

In the last question why do we write "is k not a prime number"?

Can S ever be greater than k+ 1?
gmat-admin's picture

All integers greater than 1 are either prime numbers or non-prime numbers (aka composite numbers).

All prime numbers, k, are such that the sum of their positive divisors = k + 1. For example, the divisors of 5 (a prime number) are 1 and 5. So, the sum (6) is 1 greater than 5. Likewise, the divisors of 11 (a prime number) are 1 and 11. So, the sum (12) is 1 greater than 11.

All non-prime numbers, k, are different. For them, the sum of their divisors is GREATER THAN k+1. For example, For example, the divisors of 8 (a non-prime number) are 1, 2, 4 and 8. So, the sum (15) is greater than 8+1. Likewise, the divisors of 15 (a non-prime number) are 1, 3, 5 and 15. So, the sum (24) is greater than 15+1.

So, to answer your question, S CAN be greater than k+1. In fact, if k is a non-prime number, then S is certainly greater than k+1

So, asking "Is S > k+1?" is exactly the same as asking "Is k a non-prime number?"

This lesson appears very early in the course. You'll learn more about divisors and prime number in the Integer Properties module: https://www.gmatprepnow.com/module/gmat-integer-properties

ademini's picture

Hi,
I really appreciate this whole piece. I am from Nigeria, constant light and data is an issue here. I bought your package and I am enjoying it so far. I stumbled on flashare for a lecture here, I downloaded it and found it very useful. Is it possible to be directed to where I can get more here?

Regards
gmat-admin's picture

Hi ademini,

By "flashare," do you mean SlideShare? If so, here's our SlideShare page with some more downloads: https://www.slideshare.net/GMATPrepNow_free/

Cheers,
Brent

ademini's picture

Wow!

I knew I wasnt making a mistake buying your service.
Many Thanks!!
Exactly my need. I meant slideshare, sorry.

Thanks!

Hi Brent,

in the end of the video you tell us to keep track of original and rephrased questions. How do you suggest to do this? Excel, paper, etc.? Also, do you have a file with a list like that to be downloaded?

Best,
Guilherme
gmat-admin's picture

Hi Guilherme,

You can use pen and paper, pencil and paper, Excel, Word, hieroglyphics, etc :-)
It's your choice.

I don't have a downloadable list of such questions, however if you go to the Beat The GMAT and GMAT Club forums, and perform a search for "This is a good candidate for rephrasing the target question" (a preset phrase I often type when answering Data Sufficiency questions), you'll find all of the instances in which I've rephrased the target question.

I hope that helps.

Cheers,
Brent

Hi,
First of all, loved your videos..they help in a very subtle way but nevertheless important. i have just one 'silly' doubt. It's regarding |x| < 1. Doesnt that mean x < 1, -1 or in other words, x is less than 1 and x is less than -1...if that's true, then the range will not be -1<x<1, isn't it?

gmat-admin's picture

Quote: "...in other words, x is less than 1 and x is less than -1"

That conclusion isn't correct.

We can show why it isn't correct by testing some x-values that are less than -1
For example, -2 is less than -1, so let's plug this into our given inequality, |x| < 1

We get: |-2| < 1
Evaluate to get: 2 < 1
Since 2 is not less than 1, we can see that -2 is not a possible value of x.

Here's the video on solving inequalities involving absolute value: https://www.gmatprepnow.com/module/gmat-algebra-and-equation-solving/vid...

Cheers,
Brent

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