Conference Room

Question

In a certain conference room each row of chairs has the same number of chairs, and the number of rows is 1 less than the number of chairs in a row. How many chairs are in the row? (1) There is a total of 72 chairs. (2) After one chair is removed from the last row, there is a total of 17 chairs in the last two rows. OA is D

ronniecoleman · Answer

1: N*(N-1) = 72 N = -8 , 9 N cannot be negative hence n = 9 2. ADD 1 to 17 = 18 each row will have 18/2 = 9 hence we have 9 chairs IMO D

cramya · Answer

let the rows be R
let the chairs in each row be ch

r = ch-1

Stmt I

ch * (ch-1) = 72

Possible value ch = 9 ch-1 = 8

9 chairs

SUFF

Stmt II

one chair removed makes it 17 so there were 18 chair in2 rows before removing the 1 chair

Again 9 chairs

SUFF

D)

sudhir3127 · Answer

Abdulla wrote:In a certain conference room each row of chairs has the same number of chairs, and the number of rows is 1 less than the number of chairs in a row. How many chairs are in the row? (1) There is a total of 72 chairs. (2) After one chair is removed from the last row, there is a total of 17 chairs in the last two rows. OA is C i think this is a gmat prep question and the OA has to be D . Please make sure and doubly chk the questions and Answers before u post, It unncessarily creates confusion and takes a lot of time .

Abdulla · Answer

sudhir3127 wrote:Abdulla wrote:In a certain conference room each row of chairs has the same number of chairs, and the number of rows is 1 less than the number of chairs in a row. How many chairs are in the row? (1) There is a total of 72 chairs. (2) After one chair is removed from the last row, there is a total of 17 chairs in the last two rows. OA is C i think this is a gmat prep question and the OA has to be D . Please make sure and doubly chk the questions and Answers before u post, It unncessarily creates confusion and takes a lot of time . I'm so sorry.. it was my mistake .. i didn't mean it.

vittalgmat · Answer

Yep got it .
I used one my take aways to reduce calculation and here it is.
(I am not sure if I can apply in all cases. So pls review and let me
know your feedback.)

Let the number of rows be r
stmt 1: says
r(r+1) = 72.
=> r^2 +r -72 = 0
72 is not a perfect square. So the two roots will be of opposite sign.
Dont care what it is. one of them is +ve which is what I need coz the
chairs and/or rows cannot be -ve. Therefore sufficient.
As a side note: I wonder if I can make the above conclusion.. what if the two roots are -ve something and a +ve fraction. Then both are invalid coz we cannot have fractional rows or chairs.
Am I taking a risk on the GMAT question by assuming that one of the roots will always be 'practical'??

Some one pls comment.

cramya · Answer

Am I taking a risk on the GMAT question by assuming that one of the roots will always be 'practical'??

Hard to tell.

Lets say eqn is x^2+6x+6 (6 is not a perfect square)

One distinct root but -ve.

IMO I would spend the extra 30 secs - minute to make sure it leads to the desired root to predict sufficiency.

Strictly my opinion.Hope I dint miss something in your logic above.

Regards,
Cramya

pbanavara · Answer

vittalgmat wrote:Yep got it .
I used one my take aways to reduce calculation and here it is.
(I am not sure if I can apply in all cases. So pls review and let me
know your feedback.)

Let the number of rows be r
stmt 1: says
r(r+1) = 72.
=> r^2 +r -72 = 0
72 is not a perfect square. So the two roots will be of opposite sign.
Dont care what it is. one of them is +ve which is what I need coz the
chairs and/or rows cannot be -ve. Therefore sufficient.
As a side note: I wonder if I can make the above conclusion.. what if the two roots are -ve something and a +ve fraction. Then both are invalid coz we cannot have fractional rows or chairs.
Am I taking a risk on the GMAT question by assuming that one of the roots will always be 'practical'??

Some one pls comment.

Honestly I wouldn't risk it .. when u r at this stage - it will take another 10 seconds to figure out the roots and the answer. May be 15 but I would spend the 15 secs and be sure of my answer.

- pradeep

vittalgmat · Answer

Thank you guys. I will use it with utmost care.. and may be even abandon this. good point.

vishubn · Answer

Abdulla wrote:sudhir3127 wrote:Abdulla wrote:In a certain conference room each row of chairs has the same number of chairs, and the number of rows is 1 less than the number of chairs in a row. How many chairs are in the row? (1) There is a total of 72 chairs. (2) After one chair is removed from the last row, there is a total of 17 chairs in the last two rows. OA is C i think this is a gmat prep question and the OA has to be D . Please make sure and doubly chk the questions and Answers before u post, It unncessarily creates confusion and takes a lot of time . In a way its FUN One will not prove to get to the OA rather prove it to be right Vishu I'm so sorry.. it was my mistake .. i didn't mean it.

vladmire · Answer

Can anyone explain how statement one is sufficient by itself? ***note** the number of rows is 1 less than the number of chairs in a row.

Choose how you want to prepare

Get Ready for GMAT Test Day Faster with Live Online Classes

Target Test Prep EA OnDemand

Target Test Prep GMAT OnDemand

Conference Room

Re: Conference Room

Re: Conference Room

Re: Conference Room

Rows

Chicago Booth

GMAT Course Reviews

Admissions Consulting Reviews

FREE GMAT PREP RESOURCES

GMAT PREP DEAL TRACKER