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In a certain conference room each row of chairs has the same

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

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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.

Any idea how the answer would be D?
[Reveal] Spoiler: OA

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

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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?

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

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New post 15 Nov 2015, 23:35
enigma123 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?

(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

Statement 2: C + (C-1) =17
Hence C = 9
SUFFICIENT

Option D

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

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

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New post 27 Dec 2015, 03:39
redfield wrote:
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


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.

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

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New post 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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New post 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?

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

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New post 06 Nov 2017, 20:57
cman2010 wrote:
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?


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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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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

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New post 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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Re: In a certain conference room each row of chairs has the same   [#permalink] 06 Nov 2017, 21:02
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