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Comment on The Table Method
In the x<x^2 question, can we
When we plug in x = 1, the answer to the target question is "No, x is NOT less than x^2"
Ok..thank you sir
I think there is a mistake in the exercise done at 3:30 on this video, when is said divided, he is actually doing subtraction.
Sorry to bother
Thanks for that, but
Thanks for that, but "division" is correct here. 5 divided by 3 equals 1 with remainder 2.
I would like to ask based on your experience if I could take CAT each Week or it would not reflect any changes in my progress.
If you've already reviewed
If you've already reviewed all of the GMAT content, then taking regular practice tests (CAT's) is a great idea. This will help build your test-taking skills AND help identify any remaining area(s) of weakness.
While carefully analyzing your practice tests, there are four main types of weakness to watch out for:
1. specific Quant skills/concepts (e.g., algebra, standard deviation, etc.)
2. specific Verbal skills/concepts (e.g., verb tenses, assumption CR questions, etc.)
3. test-taking skills (time management, endurance, anxiety etc.)
4. silly mistakes
For the first two weaknesses, the fix is pretty straightforward. Learn the concept/skill and find some practice questions to strengthen that weakness.
If your test-taking skills are holding you back, then you need to work on these. Be sure to review out time management video at http://www.gmatprepnow.com/module/general-gmat-strategies/video/1244
Finally, if silly mistakes are hurting your score, then it's important that you identify and categorize these mistakes so that, during tests, you can easily spot situations in which you're prone to making errors. I write about this and other strategies in the following article: http://www.gmatprepnow.com/articles/avoiding-silly-misteaks-gmat
Just getting started on these videos so maybe this will be come more clear in time, but I'm having trouble understanding sufficient/insufficient.
For example, the question at 4:25 and the statement x is positive. Doesn't this statement provide sufficient information to definitively answer "Is x < x^2?". When x = 2 we can definitively answer the question, yes, x < x^2. When x = .5 we can definitively answer the question, no, x < x^2.
If I'm remembering correctly from the previous video, we don't want to fall into the trap of answering the target question. We only want to answer whether the statement is sufficient to answer the target question. In this case, wouldn't the statement be sufficient to answer the question?
I guess I'm having trouble determining what qualifies as sufficient to answer the target question and what's just answering the target question.
Good question, Alex.
Good question, Alex.
Data Sufficiency questions can seem very strange at first. The important thing is to keep asking yourself "Does this statement provide enough information to definitively answer the target question?"
Here, the target question asks "Is x < x²?"
This is a YES/NO question, so a statement will be considered sufficient if we can definitively answer in one of the two following ways:
- YES, x IS less than x²
- NO, x is NOT less than x²
When we test two possible values of x (x = 2 and x = 0.5), we get different answers to the target question.
In the first case (x = 2), the answer is "YES, x IS less than x²"
In the second case (x = 0.5), the answer is "NO, x is NOT less than x²"
So, which is it? Is or isn't x less than x²?
We can't say for certain. So, that statement is not sufficient.
Does that help?
yup, very helpful. Thanks!
I know that the statement 1 is not sufficient because if x=1, but before to see it, don’t make sense for me because is not clear in my mind why isn't right 0.5 < 0.25. I see that 0.25 is greater than 0.5.
Be careful. 0.25 is not
Be careful. 0.25 is not greater than 0.5
0.25 = 25/100 = 1/4
0.5 = 5/10 = 1/2
1/2 of a pizza is more than 1/4
In other words, 0.5 > 0.25
Does that help?
Alex, I do understood by
What is the remainder when
I chose the number 1 and 5 as a test case which is different from what you use. Is there a strategy on choosing smart numbers?
You're referring to the
You're referring to the question at 2:40 in the above video.
Your numbers (x = 1 and x = 5) also work.
The goal with testing values is to (hopefully) find conflicting answers to the target question, which means the statement is not sufficient.
With your numbers (x = 1 and x = 5), we get just that.
If x = 1, then the answer to the target question is "The remainder is 1 when x is divided by 3"
If x = 5, then the answer to the target question is "The remainder is 2 when x is divided by 3"
Since we cannot answer the target question with certainty, the statement is not sufficient.
The next video covers how to choose good numbers to test: https://www.gmatprepnow.com/module/gmat-data-sufficiency/video/1102
Hi Brent, I understand on
Here's the question:
Here's the question:
What is the remainder when positive integer x is divided by 3?
Statement 1: When x is divided by 4 the remainder is 1
The concepts you're referring to are covered later in the course (at https://www.gmatprepnow.com/module/gmat-integer-properties/video/842).
The answer to your question depends on what you mean when you say "the statement does not have any correlation with the metrics given in the target question." can you elaborate?
In the meantime, I'll note that, IF statement 1 were "When x is divided by 6 the remainder is 1," then the statement would be SUFFICIENT.
What i mean't by correlation
Thanks for the clarification.
Thanks for the clarification.
In that case, we can't conclude that statement 1 is not sufficient just because 4 is different from 3.
Target question: What is the remainder when x is divided by 3?
Statement 1: When x is divided by 6, the remainder is 1.
This statement is sufficient because it tells us that x must be one of the following values: 1, 7, 13, 19, 25, 31, 37,....etc
Every one of those possible values leaves a remainder of 1 when divided by 3, which means we can answer the target question with certainty.
So, statement 1 is sufficient.
Does rephrasing the target
I'm assuming you're referring
I'm assuming you're referring to the question that starts at 4:15 in the above video.
TARGET QUESTION: Is x < x²
You are dividing both sides of the inequality by x, which is a bad idea, since we don't know whether x is POSITIVE or NEGATIVE.
If x is POSITIVE, then we divide both sides by x to get: Is 1 < x?
If x is NEGATIVE, then we divide both sides by x to get: Is 1 > x?
Since we don't know the sign of x, we can't divide both sides by x.
Any guidelines on when to
That skill will develop as
That skill will develop as you learn more and more concepts.
For example, later in the Algebra module, you'll learn that, in most cases, you cannot solve a linear equation for one variable.
Here's what I mean:
TARGET QUESTION: What is the value of x?
(1) x + y = 7
The equation x + y = 7 is a linear equation, which means there are infinitely many solutions to this equation (e.g., x=0 & y=7 AND x=1 & y=6 AND x=2.6 & y=4.4, etc)
So, statement 1 is not sufficient
I want to ask one thing, how are the values being plugged in the Data Sufficiency Questions? For instance, in the very first question, the first value being put is X=1 and than X=4, i find this very difficult like how you deduce to check x at 4 immediately after you check x at 1?
i need to understand how are the values chosen for any DS Question?
In the next lesson (https://www.gmatprepnow.com/module/gmat-data-sufficiency/video/1102), we discuss "good" numbers to test when using the Table Method. These are numbers that have a wide variety of properties: -10, -1, -1/2, 0, 1/2, 1 and 10
When using the Table Method, we want to test values so that we get different answers to the target question. We also want to test "easy" values that work well with the given information.
For the first question that appears in the above video, statement 1 tells us that, x is positive.
This means we can rule out testing -10, -1, -1/2 and 0.
Testing x = 1 is very easy for us, and when we do this, we find that the answer to the target question is YES.
At this point, our goal is to find an x-value that yields an answer of NO to our target question.
From here, I COULD test x = 10, but that would make our calculations very difficult (e.g., 4^10 = 1,048,576), especially since we don't have a calculator at our disposal.
So rather than test x = 10, I chose a value of x that's less than 10, but still allows me to readily calculate 4^x and 3^(x+1).
So, I chose x = 4.
Does that help?
This module is great btw. Just what I was looking for.
I had the same question when it came to selecting test cases/strategic numbers/whatever you want to call them. It's something that still hasn't clicked for me. When I saw you choose 4 immediately after 1 and get opposite results, it just seems like black magic to me.
I went back and tested 2 and 3, and still got yes answers. It's not until 4 when the relationship flips. I can't for the life of me understand why that's the case and how you knew that's where it would happen.
This is a pretty esoteric
This is a pretty esoteric point (and extremely unlikely to ever be tested on the GMAT), but one way to understand why the relationship "flips" is to examine the DIFFERENCE between 4^x and 3^(x+1) relative to the value of either 4^x or 3^(x+1).
For example, when x = 1, 4^x = 4, and 3^(x+1) = 9.
Difference = 9 - 4 = 5
When we calculate the ratio of the difference to the value of 4^x, we get: 5/4
When x = 2, 4^x = 16, and 3^(x+1) = 27.
Difference = 27 - 16 = 11
Ratio of the difference to the value of 4^x = 11/16
Notice that the ratio has decreased (from 5/4 to 11/16)
When x = 3, 4^x = 64, and 3^(x+1) = 81.
Difference = 81 - 64 = 17
Ratio of the difference to the value of 4^x = 17/64
Notice that the ratio is still decreasing (from 5/4 to 11/16 to 17/64)
All of this SUGGESTS the ratio MAY decrease so much that it eventually becomes negative (meaning the value of 4^x is greater than 3^(x+1)
Fortunately, it turns out this occurs when x = 4
Hi Brent, a quick question on
For statement number (1)Yesterday, John spent less than $25 at the store, can I assume that John could spend the money either on records or CDs? My answer was C, but seems like the answer was A.
Question link: https:/
Question link: https://gmatclub.com/forum/a-certain-store-sells-only-records-and-cds-al...
Your assumption that John could spend the money either on records or CDs is correct. However, if we examine all possible cases in which John spends less than $25, we'll see that, for every case, the answer to the target question is always the same: NO, John did NOT buy more than 5 records.
Since we can answer the target question with certainty, statement 1 is sufficient.
Does that help?