GMAT Data Sufficiency Discussions

[Govi]

The GMAT and Related Discussions section is very fragmented in terms of the information available at one's disposal. There are one of reply threads and several other redundant threads that have masked the more important ones.

This is an attempt to make the best of explanations, reasonings, questions etc etc easily available to the junta here. We would be having separate threads for topics such as

Problem Solving (GMAT Problem Solving Discussions) (the existing one is renamed)

Data Sufficieny

Sentence Correction (GMAT Sentence Correction Discussions)

Critical Reasoning (GMAT Critical Reasoning Discussions)

Reading Comprehension. (GMAT Reading Comprehension Discussions)

Please ensure that Q & As are carried out in the repsective threads.

Thread is made sticky

PS:-This post would be edited by the MODS in order to give links to various DSs that would be discussed here. We will try to organise the links for the questions discussed here.
Other relevant posts in the 'one of reply' threads would be moved here

[Govi]

Q If xyz ≠ 0, is x (y + z) ≥ 0?

(1) |y + z| = |y| + |z|
(2) |x + y| = |x| + |y|

[nitiman]

Originally Posted by Govi

Q If xyz ≠ 0, is x (y + z) ≥ 0?

(1) |y + z| = |y| + |z|
(2) |x + y| = |x| + |y|

Ans is C. Am i correct?
From (1) we can infer y and z have same sign. Similarly from (2) x and y have same signs. So combining both x, y, z have same sign. So x(y+z) is greater than 0.

[Govi]

Originally Posted by nitiman

Ans is C. Am i correct?
From (1) we can infer y and z have same sign. Similarly from (2) x and y have same signs. So combining both x, y, z have same sign. So x(y+z) is greater than 0.

Correct and well explained

Here is one more that's posted in one of threads in this forum

How many different prime factors does N have?

(1) 2N has 4 different prime factors.
(2) N ^2 has 4 different prime factors.

[Catalytic]

is it B?
1) If N already has 2 a factor then it will have 4 factors but 2 is not a factor then N would have 3 factor. So number of factors is uncertain
2) Squaring a number would not change distinct prime factors. If N^2 has 4 then N has 4

Rusty so not very sure of the answer

[Govi]

Originally Posted by Catalytic

is it B?
1) If N already has 2 a factor then it will have 4 factors but 2 is not a factor then N would have 3 factor. So number of factors is uncertain
2) Squaring a number would not change distinct prime factors. If N^2 has 4 then N has 4

Rusty so not very sure of the answer

Correct it is B to cite an example

Stem 1 - 2N can be 2 x 105 this may have prime factors viz 2, 3, 5, 7 and N will have prime factors 3, 5, 7 OR 2N can be 2 x 210 this may have prime factors 2, 3, 5, 7 and N will have prime factors 2, 3, 5, 7. Insufficient

Stem 2 - Sufficient and reasoning as provide above

[aim-wsc]

Anybody interested sharing his/her DS strategies?

[Govi]

Originally Posted by aim-wsc

Anybody interested sharing his/her DS strategies?

@aim Keep posting questions and I am sure many would join in with their strategies and approach.

[Govi]

Q. The integers m and p are such that 2<m<p and m is not a factor of p. If r is the remainder when p is divided by m, is r > 1 ?

1. the greatest common factor of m and p is 2

2. the least common multiple of m and p is 30

[nitiman]

Originally Posted by Govi

Q. The integers m and p are such that 2<m<p and m is not a factor of p. If r is the remainder when p is divided by m, is r > 1 ?

1. the greatest common factor of m and p is 2

2. the least common multiple of m and p is 30

Is it D?
According to first statement and given data if m=n then p is also even and n+2=< p =<2n-2. In this case the remainder can be anything between 2 to 2n-2 which is always greater than 1.
According to sec statement LCM of m and p is 30. Factors of 30 are 1, 2, 3, 5, 6, 10, 15, 30. m>2 So possible values of m and p are 3 and 10 or 5 and 6 and in both the cases remainder is 1.
So both statements are individually sufficient.