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In a certain conference room each row of chairs has the same [#permalink]

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20 Mar 2012, 09:30

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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 a row?

(1) There is a total of 72 chairs. (2) After 1 chair is removed from the last row, there is a total of 17 chairs in the last 2 rows.

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 a row?

Say # of rows is R and # of chairs per row is C. Given: R=C-1. Question: C=?

(1) There is a total of 72 chairs --> CR=72 --> C(C-1)=72 --> C=9. Sufficient.

(2) After 1 chair is removed from the last row, there is a total of 17 chairs in the last 2 rows --> C+(C-1)=17 --> C=9. Sufficient.

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 a row?

(1) There is a total of 72 chairs. (2) After 1 chair is removed from the last row, there is a total of 17 chairs in the last 2 rows.

Any idea how the answer would be D?

Given: Number of rows is 1 less than the number of chairs in a row and each row has same number of chairs. Assuming the number of Chairs = C. Number of rows = C-1

Required: C = ?

Statement 1: Total chairs = 72 Total chairs = (chairs in a row)*(number of rows) = C*(C-1) C*(C-1) = 72, Hence C =9 SUFFICIENT

Re: In a certain conference room each row of chairs has the same [#permalink]

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26 Dec 2015, 14:57

Bunuel 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 a row?

Say # of rows is R and # of chairs per row is C. Given: R=C-1. Question: C=?

(1) There is a total of 72 chairs --> CR=72 --> C(C-1)=72 --> C=9. Sufficient.

How do we calculate C(C-1)=72? Doesn't that become C^2-C =72? What is the next step there
_________________

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 a row?

Say # of rows is R and # of chairs per row is C. Given: R=C-1. Question: C=?

(1) There is a total of 72 chairs --> CR=72 --> C(C-1)=72 --> C=9. Sufficient.

How do we calculate C(C-1)=72? Doesn't that become C^2-C =72? What is the next step there

There is an easier way. Since C must be a positive integer, then C(C-1) is the product of 2 consecutive integers. The product of 2 consecutive integers equal to 72 is 9*8.

Re: In a certain conference room each row of chairs has the same [#permalink]

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12 Jan 2017, 17:24

Let number of rows is a, number of the chairs in a row is b. So, b-a=1 From 1, ab72, a8, b9, sufficient alone. From 2, 2b-1=17, b=9, sufficient alone. Answer is D.
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Re: In a certain conference room each row of chairs has the same [#permalink]

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06 Nov 2017, 17:28

Bunuel 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 a row?

Say # of rows is R and # of chairs per row is C. Given: R=C-1. Question: C=?

(1) There is a total of 72 chairs --> CR=72 --> C(C-1)=72 --> C=9. Sufficient.

(2) After 1 chair is removed from the last row, there is a total of 17 chairs in the last 2 rows --> C+(C-1)=17 --> C=9. Sufficient.

Answer: D.

Where does "C(C-1)" come from? Why aren't you just plugging 72 into the equation C-1=R?

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 a row?

Say # of rows is R and # of chairs per row is C. Given: R=C-1. Question: C=?

(1) There is a total of 72 chairs --> CR=72 --> C(C-1)=72 --> C=9. Sufficient.

(2) After 1 chair is removed from the last row, there is a total of 17 chairs in the last 2 rows --> C+(C-1)=17 --> C=9. Sufficient.

Answer: D.

Where does "C(C-1)" come from? Why aren't you just plugging 72 into the equation C-1=R?

We are told that the number of rows is 1 less than the number of chairs in a row. So, if the number of chairs per row is C, then the number of rows is C - 1 and thus the total number of chairs is (the number of chairs per row)*(the number of rows) = C(C-1).
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Re: In a certain conference room each row of chairs has the same [#permalink]

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06 Nov 2017, 21:02

From A There is a total of 72 chairs. So it should be 9*8 Sufficient From B After 1 chair is removed from the last row, there is a total of 17 chairs in the last 2 rows. last 2 total is enough to calculate So sufficient.
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Regards, Naveen email: nkmungila@gmail.com Please press kudos if you like this post