I would be very grateful if people provided explanations for

Question

I would be very grateful if people provided explanations for the attached GMATPrep problems. The official answer is the option that is highlighted in blue with a square.
 
Thank you in advance.

SimaQ · Answer

II question....

We know the two lenghts of the triangular is 5 and 2.
The key here is to keep in mind that the sum of any two sides of the triangular cannot be less than the length of the remaining side....

So..

I) asks if the the perimeter could be equal to 9.
No, because 5+2+2=9, 2+2=4 which is <5

II) perimeter = 15
No, because 5+2+8=15, but 5+2=7 which is <8

III) perimeter = 19
No, because 5+2+12=19, but 5+2=7 which is <12

SimaQ · Answer

Cannot provide you with the good explanation of I question.... Simply picked some numbers identified a pattern and chose the right answer...

laxieqv · Answer

to be explicit, let a, b and c be the three sides 
Assign a, b to the two known sides.
c must satisfy the condition that is:
|a-b| < c< a+b 

(| | is used here because we don't know if a> b or vice versa)

Apply this rule, the third side must be in the range from 3 to 7 exclusively

so the perimeter must be from 10 to 14

None of the choices satisfies.

Nayan · Answer

Expln of 1st qn:

LCM of x,6,9

stmt 1: LCM of x and 6 is 30.
So LCM of x,6,9 is the same as the LCM of 30 and 9
Suf

stmt 2:
Same as above, if you know the LCM of 2 umbers, The LCM of that LCM and the third number is the LCM of all the three.
Suf

So D.

vivek123 · Answer

1) For LCM question.
 I go for "D"

2) For perimeter question
None of these!

I would be very grateful if people provided explanations for

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