Regarding Yes/No Data sufficiency

[Sabari Senthil]

Hi,

This is sabari.

I am planning to give my GMAT Exam on march 15.

I am finding out difficulties while solving the Yes or No Data Sufficiency Questions.

I'll be happy if i got any documents for free of cost for solving these type of problems.

I am waiting for ur comments for solving out these type of problems.

Please find some of the problems below that i found difficulties....


1)If xy< 3, is x < 1?
i)y > 3
ii)x <3

2)What is the value of [positive integer n?
i)n^4 < 25
ii)n is not equal to n^2

[Grumppee17]

If xy < 3, is x < 1?

(1) y > 3

You can start off by testing some values and plugging them into the equation they give us. So we know y has to be greater than 3. Let's pick some values for y. 4 , 5, 10 and 15.

Notice that when we plug in these values into the equation, we get: 4x<3, 5x<3, 10x<3 and 15x<3. When we solve for x respectively for these values, we will get x < .75, .60, .30, and .20. Which are all less than 1 and keep getting farther away from 1 as y gets bigger. So when y >3, x is in fact < 1. So that is a YES for this statment. We've ruled out B, C, E.

(2) x < 3

For this statement, x could be less than 1. We're almost tempted to fly over this one. But x could be 2 as well. Since we have a YES and a NO....this statement is insufficient.

And I believe the answer to this question is A.

[tmmyc]

2)What is the value of positive integer n?

i)n^4 < 25

Since n is a positive integer, let's see which integer(s) fit this criteria starting with the smallest.
1^4 = 1 < 25 YES
2^4 = 16 < 25 YES
3^4 = 81 < 25 NO - We can stop here because every other positive integer will be larger than this.

Since n can be either 1 or 2, this statement is insufficient. (Cross out choices A and D)


ii)n is not equal to n^2

This is easily identifiable since for positive integer n where n equals n^2, n can only be 1 (1 = 1^2).
Choose any other positive integer and n will not equal n^2. (2 != 2^2; 3 != 3^2; etc.)
Since n can be any positive integer greater than 1, this statement is also insufficient. (Cross out choice B)


TOGETHER

The first statement limits the choices to either 1 and 2. The second statement limits the choices to any positive integer greater than 1. Thus, the statements taken together are sufficient and n must be 2.

The answer is C.

[StaceyKoprince]

Please cite the source of these two questions; if you don't, we will have to delete the questions and any commentary on them.

For yes/no questions, be aware first of all that a definitive yes answer is sufficient and a definitive no answer is sufficient. Only sometimes yes / sometimes no is insufficient.

Also, as the posters above noted, when you can try real numbers, go ahead and try real numbers! Just make sure to try different kinds of numbers (positive and negative integers, fractions between zero and one, 0, 1).

Finally, follow whatever constraints the problem gives you. Except for the exact question itself (eg, is x = 1?), you have to accept all other information as true (eg, "if x is positive" in the question stem). The two statements we always accept as true - you can only try numbers that make those two statements true.